Direct reaction experiments with exotic beams (Keynote Talk)

• Daniel Bazin (Michigan State University)

Room: Scotiabank Theatre Performing direct reaction experiments using rare isotope beams with very low intensities such as those presently or projected to be available at facilities around the globe is challenging. Techniques and methods to utilize these sparse beams in the most optimum way are essential to the progress of nuclear science. Among these techniques two approaches are well adapted to two different energy domains: knockout reactions on fast beams produced via projectile fragmentation, and using an active target detector to maximize the luminosity at energies close to the Coulomb barrier. Although knockout reactions have been used extensively for over a decade, the details of the underlying reaction mechanism has only recently been explored experimentally. Results of exclusive experiments demonstrate the robustness of our understanding of such reactions, and validate their use as a spectroscopic tool. These reactions were recently used to measure one-nucleon removal cross section with a 5% precision on radioactive p-shell nuclei and interpret the results in relation to ab-initio calculations of spectroscopic factors. At energies close to the Coulomb barrier, reactions in inverse kinematics are plagued by the difficulty to efficiently and precisely measure the characteristics of the emerging particles. The Active Target Time Projection Chamber (AT-TPC) used at the NSCL and elsewhere offers an elegant solution to this dilemma, and promises to advance our reach towards very exotic nuclei produced as radioactive beams. One particularly interesting avenue is the use of resonant scattering experiments to probe the spectroscopic and cluster properties of the projectile+target composite systems.

Recent progress and future perspectives in the theory of direct reactions and exotic nuclei (Keynote Talk)

• Sofia Quaglioni (LLNL)

Room: Scotiabank Theatre As existing and upcoming radioactive ion beam facilities promise unprecedented access to a vast new array of exotic phenomena, a complete understanding of nuclei and their role in the cosmos cannot be achieved without a solid connection between measured reaction observables and predictions of nuclear structure theory. This requires practical, yet robust models of direct nuclear reactions and a clear understanding of their limits of applicability. In this talk I will present an overview of recent progress in the theory of direct reactions with exotic nuclei, as well as an example of how ab initio calculations are starting to bridge the gap between structure and reactions in light exotic nuclei. I will then reflect on future perspectives of the field.

Competing particle-hole excitations in $^{30}$Na: constraining state-of-the-art effective interactions (Invited)

• Marina Petri (Technical University Darmstadt)

Room: Scotiabank Theatre Light neutron-rich nuclei around N=20 show properties that are not in line with their expected magicity but rather imply a deformed shape. These nuclei lie in the so-called ''Island of Inversion'' where the deformation is due to neutron cross-shell excitations dominating their ground and low-lying states. Recently, there has been much interest in studying the transition towards this region to determine the evolution of the sd-pf shell gap around N=20 and to provide a stringent test for nuclear models. In this work the odd-odd nucleus $^{30}$Na is studied via 1p, 1p1n and 1n knockout reactions at the NSCL using $^{31}$Mg, $^{32}$Mg and $^{31}$Na radioactive beams, respectively. Combining high-resolution $\gamma$-ray spectroscopy with the selectivity of the various reaction mechanisms we are able to distinguish multiple particle-hole configurations. Negative parity states in $^{30}$Na are observed for the first time, providing an important measure of the excitation of the 1p1h configuration and hence the sd-pf shell gap. Extracted band structures and level energies are compared with state-of-the-art shell model calculations.

Quasi-free proton knockout of $^{23,25}$F (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Tsz Leung Tang (RCNP)

Room: Scotiabank Theatre The spectra of proton separation energy of $^{23,25}$F were measured by (p,2p) quasi-free scattering. The spectroscopic factors (SF) of the proton bounded states were deduced by comparing with a DWIA calculation. We found that SF the 1d$_{5/2}$ proton of $^{23}$F and $^{25}$F are 0.4 ± 0.1 and 0.9 ± 0.2 respectively. The deformation of $^{23}$F nucleus may be the reason for the reduction. The result of $^{25}$F can be understood as a result of the double magic of $^{24}$O. We have demonstrated a (p,2p) knockout reaction for probing the bounded states on neutron rich nucleus $^{23}$F and $^{25}$F. The $^{23,25}$F were produced by BigRIPS in RIKEN Nishina Center, Radioactive Isotope Beam Facility at 289A MeV and 277A MeV respectively. The proton separation energy was extracted by reconstructing the missing 4-momentum of oxygen residue by detecting the scattered protons. We managed to decompose the energy spectrum by selecting different oxygen isotopes, which were results of multi-neutrons emission of highly excited oxygen residue. The reason for small sum of spectroscopic factors for the s-d shell proton of $^{23}$F is not clear. The overall effect from the nuclear structure and reaction mechanism due to deformation is still unknown. In contrast, the sum of spectroscopic factors of the s-d shell proton of $^{25}$F is closed to unit and indicates that it is a single particle orbit. The agreement of the reduction factor in the trend of the $R_{S}−\Delta S$ plot could be due to limitation of 1-neutron threshold. Also, the large reduction factor for the p-shell in both $^{23}$F and $^{25}$F shows that the trend depends on analysis method.

Spins and decays in neutron-rich sodium isotopes via (d,p$_{\gamma}$) (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Wilton Catford (University of Surrey)

Room: Scotiabank Theatre Using neutron transfer reactions, the evolution in energy of single-particle levels can be studied whether they are occupied or not, in the ground state of the final nucleus. Therefore, the levels of interest in the development of the island of inversion at N=20 and the emergence of the magic numbers N=16, 32 and 34 can be studied via excited states in less neutron-rich isotopes. The excited states of interest need to be not too high in energy and, ideally, bound to gamma-ray decay. We have completed a detailed study of $^{26}$Na using an intense beam of $3 \times 10^7$ pps $^{25}$Na at 5 MeV/nucleon obtained from ISAC2 at TRIUMF. The experiment used the SHARC array of DSSDs with the TIGRESS gamma-ray array. States in $^{26}$Na that were closely spaced in excitation energy were separated experimentally using the Doppler-corrected gamma-ray energy. Differential cross sections were extracted with gating on the gamma-ray energy. A detailed study was performed of the possible biasing effects of the gamma-ray gating and methods for dealing with this were devised. As an essential part of the analysis, gamma-ray branching ratios for all of the observed states were measured. In a further study using a beam of $^{24}$Na ions at 8 MeV/nucleon our knowledge of the structure of $^{25}$Na has been greatly extended, thanks to the highly selective population of states in neutron transfer. The angular momentum transfer and gamma-ray branching ratios have been measured for many bound states in $^{26}$Na, extending our earlier analysis that concentrated on just the states gamma-deacying directly to the ground state. It has been possible to identify the experimental counterparts to almost all of the bound states predicted by shell model calculations, including negative parity states, and to extract spectroscopic factors in most cases. For $^{25}$Na the analysis is more preliminary, but the population of final states shows good agreement with shell model expectations. Overall, there is excellent agreement with (0+1)$\hbar \omega ~$ shell model predictions obtained using the WBC interaction which includes the USD-A interaction in the $sd$-shell. In each of these Na isotopes, almost nothing was known about the excited states apart from some excitation energies, prior to the present work. This work demonstrates explicitly the enormous potential of (d,p) studies with HPGe arrays, provided that radioactive beam facilities are able to provide beams of $10^5$ to $10^7$ pps at the appropriate energies.

$^{13}$Be studied by (p,2p) deep inelastic scattering reaction in complete kinematics (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Olof Tengblad (IEM - CSIC)

Room: Scotiabank Theatre During the past three decades nuclear physics research has become more and more directed towards the understanding of the intricate properties of nuclei in the drip-line regions. The R3B instrumentation constitutes a universal fixed-target set-up with the detection and identification of incoming beam as well as of all outgoing charged particles, neutrons, and gamma rays and thus making possible complete inverse-kinematics reaction-experiments using relativistic RIBs @ 300–1500 MeV/u. Experiments with the most exotic and short-lived nuclei produced in the reaction-target and analysed in the super-FRS before reaching the set-up allows for experiments exploring the isospin frontier at and beyond the drip-lines. One of the future activities of the R3B experiment at FAIR will be to study the neutron drip-line by the use of Deep Inelastic Scattering Reactions. First experiments have already been performed using the ALADIN-LAND set-up at GSI. In this contribution we report on the structure of the unbound nucleus $^{13}$Be measured in complete kinematics using an incoming 14B beam at 490 MeV/u. Resonant states have been populated in $^{13}$Be using the selective (p,2p) channel under quasifree scattering conditions for the first time. Further, prompt gamma rays emitted in the reaction in coincidence with the fragments of interest was detected and used to interpret the structure of $^{13}$Be. This work was supported by the Spanish Ministry of Economy and Competitively MINECO under project number FPA2012-32443.

Structure of nuclei into the island of inversion from knockout reactions: $^{30,31}$Mg (Shell evolution through direct reactions)

• Beatriz Fernandez Dominguez (USC)

Room: Scotiabank Theatre B. Fernández–Domínguez$^{a,b,c,d}$, B. Pietras$^{a}$, W.N. Catford$^{e}$, N.A. Orr$^{c}$, M. Petri$^{a}$, M. Chartier$^{a}$, S. Paschalis$^{a}$, N. Patterson$^{e}$, J.S. Thomas$^{e}$, N.L. Achouri$^{c}$, J-C. Angelique$^{c}$, N.I. Ashwood$^{f}$, A. Banu$^{g}$, B. Bastin$^{c}$, R. Borcea$^{h}$, J. Brown$^{i}$, M. Caamaño$^d$, S. Franchoo$^j$, M. Freer$^f$, L. Gaudefroy$^b$, M. Labiche$^k$, B. Laurent$^c$, R.C. Lemmon$^k$, F. Negoita$^l$, E. Paul$^a$, A. Poves$^m$, P. Roussel-Chomaz$^b$, M. Staniou$^h$, M. Taylor$^i$, L. Trache$^g$,1, G. Wilson$^e$ $^a$ Univ. of Liverpool, $^b$GANIL, $^c$LPC, $^d$Univ. de Santiago de Compostela, $^e$Univ. of Surrey, $^f$Univ. of Birmingham, $^g$ Texas A&M, $^h$GSI, $^i$Univ. of York, $^j$IPNO, $^k$ CCLRC Daresbury Laboratory, $^l$IFIN-HH $^m$ IFT-UAM/CSIC The so-called ''island of inversion'' region of the nuclear chart, where transitions from normal to intruder ground state configurations across the $N = 20$ shell gap occur, has been of great interest in nuclear structure studies. Over the last decade, many experimental [1-4] and theoretical efforts [5-6] have been made along the Z=12 chain, which provide evidence that $^{31}$Mg lies inside the ''island of inversion'' whereas $^{30}$Mg and $^{29}$Mg are outside the region. The study of the single-neutron knockout reaction of $^{31}$Mg is a very interesting case since it is in the region where dramatic changes in the single-particle structure have been predicted. Indeed, $^{31}$Mg is the only magnesium isotope between the normal, $sd$ shell dominated configuration of $^{30}$Mg, and the onset of the island of inversion at $N=19$, reflecting a rather abrupt border. In spite of extensive studies on these nuclei [1-4,7-12] there are still open questions regarding the amount of mixing of the different N$\hbar\omega$ configurations. The spectroscopic factors of the populated positive and negative parity states will allow to quantify the extent of the intruder admixtures. These results are important to refine the residual interaction within shell model calculations. The ground state configuration of $^{31}$Mg nucleus has been studied using the one-neutron knockout reaction $^{12}$C($^{31}$Mg,$^{30}$Mg+$\gamma$)X. We report on the preliminary results of an experiment performed with the EXOGAM array coupled to the SPEG spectrometer at GANIL. Exclusive cross sections and longitudinal momentum distributions for the measured bound states will be presented. These results are compared to shell model calculations in the $sd$-$pf$ region [6]. [1] G. Neyens et al., Phys. Rev. Lett. 94, 022501 (2005) [2] M. Kowalska et al., Phys. Rev. C 77, 034307 (2008) [3] F. Marechal et al., Phys. Rev. C 72, 044314 (2005) [4] J. R. Terry et al., Phys. Rev. C 77, 014316 (2008) [5] M. Kimura, Phys. Rev. C 75, 041302(R) (2007) [6] E. Caurier, Phys. Rev. C 90, 014302 (2014) [7] P. Baumman et al., Phys. Rev. C 39, 626, (1989) [8] O. Niedermaier et al., Phys. Rev. Lett. 94, 172501 (2005) [9] H. Mach et al., Eur. Phys. J. A 25, s01 105-109, (2005) [10] W. Schwerdtfeger et al., Phys. Rev. Lett. 103, 012501, (2009) [11] A. N. Deacon et al., Phys. Rev. C. 82, 034305, (2010) [12] N. Imai et al., Phys. Rev. C 90, 011302(R) (2014)

Ab initio structure and reactions of light nuclei (Invited)

• Guillaume Hupin (CEA)

Room: Scotiabank Theatre Advances in the fundamental description of the interaction among nucleons in many-body techniques and in scientific computing have opened new avenues for modeling low-energy light-ion structure and reactions on an equal footing. Starting from chiral effective interactions, which provide a systematic and improvable scheme based on the underlying theory of QCD, and equipped with an *ab initio* method, we are now able to arrive at accurate evaluations of crucial reaction data for nuclear astrophysics, fusion-energy research, and other applications, and, further provide a realistic description of reactions involving exotic nuclei. I will present in this talk the No-Core Shell Model with Continuum formalism [1], which combines square-integrable $A$-nucleon eigenstates and continuous binary and ternary cluster states [2,3]. This method can accurately describe reactions in systems with more than four nucleons starting from two- and three-nucleon interactions. I will briefly review the physics cases recently unraveled by the method such as the impact of three-nucleon forces on low-energy structure and reactions. I will illustrate the method with the most comprehensive study of the $A{=}5$ and $A{=}6$ continuum ($N$-$^4$He and $d$-$^4$He elastic collisions [4,5] and the $d(t,\alpha)n$ transfer channels [6]). Finally, I will show the importance of the three-nucleon force for the description of nuclei close to the drip line, which will be exemplified with the differential cross-section of $^{10}$C$(p,p)^{10}$C. 1. S. Baroni, P. Navrátil and S. Quaglioni [Phys. Rev. Lett. **110**, 022505 (2013)][1]; [Phys. Rev. C **87**, 034326 (2013)][2]. 2. S. Quaglioni and P. Navrátil, [Phys. Rev. Lett. **101**, 092501 (2008)][3]; [Phys. Rev. C **79**, 044606 (2009)][4]. 3. S. Quaglioni, C. Romero-Redondo and P. Navrátil, [Phys. Rev. C **88**, 034320][5]; C. Romero-Redondo, S. Quaglioni, P. Navrátil and G. Hupin, [Phys. Rev. Lett. **113**, 032503 (2014)][6] 4. G. Hupin, J. Langhammer, P. Navrátil, S. Quaglioni, A. Calci and R. Roth, [Phys. Rev. C **88**, 054622 (2013)][7]; G. Hupin, S. Quaglioni, and P. Navrátil, [Phys. Rev. C **90**, 061601 (2014)][8] 5. G. Hupin, S. Quaglioni, and P. Navrátil, [Phys. Rev. Lett. **114**, 212502 (2015)][9]. 6. P. Navrátil and S. Quaglioni, [Phys. Rev. Lett. **108**, 042503][10] [1]: http://dx.doi.org/10.1103/PhysRevLett.110.022505 [2]: http://dx.doi.org/10.1103/PhysRevC.87.034326 [3]: http://dx.doi.org/10.1103/PhysRevLett.101.092501 [4]: http://dx.doi.org/10.1103/PhysRevC.76.064316 [5]: http://link.aps.org/doi/10.1103/PhysRevC.88.034320 [6]: http://link.aps.org/doi/10.1103/PhysRevLett.113.032503 [7]: http://dx.doi.org/10.1103/PhysRevC.88.054622 [8]: http://dx.doi.org/10.1103/PhysRevC.90.061601 [9]: http://link.aps.org/doi/10.1103/PhysRevLett.114.212502 [10]: http://link.aps.org/doi/10.1103/PhysRevLett.108.042503

Deformation and halo structure through reaction cross sections (Exotic structures through direct reactions)

• Shin Watanabe (Kyushu University)

Room: Scotiabank Theatre We deduce the ground-state properties of neutron-rich Mg isotopes through analyses of recently-measured reaction cross sections ($\sigma_\mathrm{R}$) [1], and then reanalyze the so-called "island of inversion (IoI)". The IoI is the region of Ne, Na, and Mg isotopes around the neutron number $N=20$-$22$. The nuclei in the IoI have exotic properties induced by the rapid shell evolution, and the elucidation is still an important subject. Our analyses are based on optical potentials constructed by the double folding model and densities calculated by antisymmetrized molecular dynamics (AMD). This framework, which does not assume nuclear structures such as deformation, enables us to calculate various observables microscopically. Our framework reproduces the measured $\sigma_\mathrm{R}$ well, and we can then deduce the ground-state properties (spin parity, total binding energy, and deformation) of Mg isotopes properly. By combing the present study on Mg isotopes[2] with the previous study on Ne isotopes[3], we find that there exists large deformation beyond the IoI from $N=19$ ($^{31}$Mg and $^{29}$Ne) to $N=28$ ($^{40}$Mg). This is consistent with the fact that the $E(4+)/E(2+)$ ratios for $^{34,36,38}$Mg deduced from in-beam $\gamma$-ray spectroscopy are about $3.1$ independently of $N$ [4]. The result indicates that the so-called island of inversion may be enlarged by melting of both the $N=20$ and $28$ magicities. Furthermore, we investigate $^{37}$Mg as a halo nucleus with a deformed $^{36}$Mg core, i.e. deformed halo nucleus. In fact, the measured $\sigma_\mathrm{R}$ on $^{37}$Mg is fairly large compared with our calculation, which already includes deformation effects. In this talk, we would also like to discuss weak-binding effects and general properties of one-neutron halo nuclei from the view point of $\sigma_\mathrm{R}$. [1] M. Takechi et al., Phys. Rev. C 90, 061305(R) (2014). [2] S. Watanabe et al., Phys. Rev. C 89, 044610 (2014). [3] T. Sumi et al., Phys. Rev. C 85, 064613 (2012). [4] P. Doornenbal et al., Phys. Rev. Lett. 111, 212502 (2013).

Extension of the ratio method to low energy and charged hal\oe s (Exotic structures through direct reactions)

• Frederic Colomer (Université Libre de Bruxelles (ULB))

Room: Scotiabank Theatre The ratio method is a recent observable that has been proposed for the study of halo nuclei [1]. It consists of the ratio of breakup angular distribution and the summed angular distribution (which includes elastic, inelastic and breakup). This removes the reaction process dependence, making it model independent. Originally, this method was developed for high and intermediate energies. Studies of the reactions of $^{11}$Be neutron-halo nucleus on $^{12}$C and $^{208}$Pb targets at 70 MeV/u have shown this observable to provide precise information about the halo structure [2]. Given the potential interest in applying this method at lower energy, we explore its validity at beam energies of 20MeV/u in this work. We use the Continuum Discretized Coupled Channel method (CDCC) and the Coulomb-corrected Dynamical Eikonal Approximation (CC-DEA) for the study of the reactions of $^{11}$Be on $^{12}$C, $^{40}$Ca and $^{208}$Pb at 20MeV/u. We analyse the influence of the projectile theoretical description on this observable and we explore the dependence of our results on the core-target interaction. Our study demonstrates that the ratio method is still valid at these lower beam energies [3]. This could open up the way to its experimental testing in ISOL-type laboratories. Moreover, we explore the validity of the method in the case of proton hal\oe s. We use CC-DEA to study the reaction of $^{8}$B proton-halo nucleus on $^{12}$C and $^{208}$Pb at 44MeV/u. Surprisingly, the ratio observable remains valid for charged hal\oe s. This result could open the method to any loosely-bound quantal system (nucleus, atom, molecule), whether charged or not. [1] P. Capel, R. C. Johnson, and F. M. Nunes, Phys. Lett. B705, 112 (2011). [2] P. Capel, R. C. Johnson, and F. M. Nunes, Phys. Rev. C 88, 044602 (2013). [3] F. Colomer, P. Capel, F. M. Nunes and R. C. Johnson, submitted to Phys. Rev. C. in Dec. 2015.

Shell evolution and spectroscopic factors (Shell evolution through direct reactions)

• Takaharu Otsuka (University of Tokyo)

Room: Scotiabank Theatre The shell evolution can create various structure patterns, of which the closed-shell structure is of particular interest. Obviously, the closed shell appears if the proton and neutron numbers coincide with magic numbers. It has been known that magic numbers vary as a consequence of the shell evolution due to nuclear forces. Thus, it is of much importance to find where the closed shell appears on the nuclear chart. The 2+ energy systematics can be a good indicator of the closed shell. On the other hand, the 2+ level reflects many aspects of nuclear forces as well as the shell structure. It is therefore crucial to have additional quantity as a measure of the magicity. We recently proposed “magic index”. This quantity implies how much fraction of the ground-state wave function is composed of the closed-shell configuration. Since correlations occur in shell-model wave functions in general, the magic index cannot be 100%. It depends also on the model space. Within a common or similar model space, the magic index can make sense. For instance, the magic index shows interesting variation among three double-magic nuclei $^{56,68,78}$Ni. It shows rather high value for $^{52,54}$Ca, while their 2+ level is not as high as $^{48}$Ca. As the magic index can be measured as spectroscopic factors, it may provide many interesting cases with transfer reactions.

Two-neutron decay of $^{16}$Be in a three-body model (Theoretical developments of direct reactions)

• Amy Lovell (NSCL/MSU)

Room: Scotiabank Theatre Recently, two-proton and two-neutron decays have become the focus of both experiment [1] and theory [2]. A 2012 experiment at the National Superconducting Cyclotron Laboratory saw the first measurement of a dineutron decay, from the neutron-rich nucleus $^{16}$Be [3]. Based on fits to the two-neutron energy and the opening angle between the two neutrons, it was claimed that $^{16}$Be decays to $^{14}$Be by a dineutron decay. $^{16}$Be is ideal for simultaneous two-neutron decay as a lower limit to the ground state of $^{15}$Be was set at 1.54 MeV [4], making the ground state in $^{15}$Be energetically inaccessible for a sequential decay. Although an $l=2$ state was observed in $^{15}$Be [5] at 1.8 MeV, very little is known about this nucleus. Depending on the width of this intermediate state, sequential decay could still be possible. Three-body models are often used to study such systems as they allow exact treatment of the degrees of freedom relevant for the decay. In our three-body system, $^{14}$Be + n + n, the degrees of freedom in the core are frozen, and it is therefore important to accurately reproduce the two-body subsystems with suitable nn and n-$^{14}$Be effective interactions. These interactions are often constrained by experimental data; however, since there has only been one level observed in $^{15}$Be [5], we rely on shell model calculations to fix the other partial waves of the n-$^{14}$Be interaction. Three-body interactions are typically included to account for the extra binding that is missing when the degrees of freedom in the core are removed. Occupied states in the core and anti-symmetrization between the two valence neutrons must also be taken into account. In this work, the three-body Schr\"odinger equation is solved using hyperspherical harmonics and the R-matrix method, from which resonance energies and widths are extracted. [6] Here, we will present our calculations for the resonant ground state of $^{16}$Be, assuming a $d_{5/2}$ or $s_{1/2}$ ground state in $^{15}$Be. We will discuss the convergence of the system, which requires a significantly larger model space than bound state calculations using similar methods (for example, [7]). Also, we will investigate the role of the nn interaction in this system, giving insight into future work that can further our understanding of the decay in two-neutron systems, both in $^{16}$Be as well as in other neutron-rich nuclei. References: [1] Z. Kohley, et. al., Phys. Rev. Lett. 108, 152501 (2013) [2] K. Hagino and H. Sagawa, Phys. Rev. C 89, 014331 (2014) [3] A. Spyrou, et. al., Phys. Rev. Lett. 108, 102501 (2012) [4] A. Spyrou, et. al., Phys. Rev. C 84, 044309 (2011) [5] J. Snyder, et. al., Phys. Rev. C 88, 031303(R) (2013) [6] A.E. Lovell, F.M. Nunes, and I.J Thompson, EPJ Web of Conferences, accepted [7] F.M. Nunes, J.A. Christley, I.J. Thompson, R.C. Johnson, and V.D. Efros, Nucl. Phys. A 609, 43 (1996) Presenter is a PhD student.

Probing nuclear structure with hydrogen-induced reactions : recent studies at the Radioactive Isotope Beam Factory, RIKEN (Invited)

• Alexandre Obertelli (CEA Saclay, RIKEN Nishina Center)

Room: Scotiabank Theatre Magic numbers of nucleons are not universal across the nuclear landscape and evolve as a function of neutron-to-proton ratio. The past years have produced vigorous work on the study of structure evolution : some historial magic numbers have been shown to disappear away from stability, while new magic numbers have been claimed. The role of different facets of the NN and NNN interactions to explain the nuclear structure evolution with isospin have been shown to be importante. Despite continuous efforts, the picture of the nuclear shell structure is not yet established experimentally nor theoretically. Spectroscopy via reactions such as quasifree scattering, (in)elastic scattering and nucleon transfer with simple-structure targets (proton, deuteron, triton) are believed to provide reliable spectroscopic information from the measured cross sections to individual final states. Along this line, recent studies performed at the RIBF will be presented. The medium-mass and heavy mass short lived nuclei are poorly known experimentaly and have to be further investigated in the coming years. First observables such as first 2+ excited states in even-even nuclei are key to explore ne regions of the nuclear landscape and draw a first picture of nuclear structure. The Radioactive Isotope Beam Factory in Japan has been for the last decade the main player in this important area. The SEASTAR collaboration performed the in-beam gamma spectroscopy of key neutron-rich nuclei at the limit of what can be done today with the use of the MINOS device [1] in combination with the DALI2 scintillator array [2]. Nuclei of interest have been produced by one and two-proton removal form a thick liquid hydrogen target. An overview of the program and recent results [3] will be shown. Inelastic scattering data shed new light on the role of neutron excitations in the collectivity of light Sn isotopes [4], that has been interpreted with help of new QRPA calculations with the Gogny D1S force [5]. Inclusive cross sections for C and H induced knockout come out to be very similar (2.1 and 2.6 mb, respectively) [6]. New transitions have been observed in 102,104Sn [7]. [1] A. Obertelli et al., Eur. Phys. J. A 50, 8 (2014). [2] S. Takeuchi et al., Nucl. Instr. Meth. A 763, 596 (2014). [3] C. Santamaria et al., Phys. Rev. Lett. 115, 192501 (2015). [4] A. Corsi et al., Phys. Lett. B 735, 127 (2014). [5] M. Martini, S. Péru, M. Dupuis, Phys.Rev. C 83, 034309 (2011). [6] L. Audirac et al., Phys. Rev. C 88, 041602(R) (2013). [7] A. Corsi et al., in preparation (2016).

Structure of $^{110}$Zr - first spectroscopy and its implications for shell evolution and the r-process (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Nancy Paul (CEA Saclay)

Room: Scotiabank Theatre A predicted Z=40 subshell closure in $^{110}$Zr has long been considered a potential explanation for the excess of elemental abundances before the A=130 r-process peak. We performed the first spectroscopy of this nucleus at the RIKEN-RIBF facility, populating the low-lying levels via (p,2p) knockout and measuring the energies with the MINOS tracker and DALI2 NaI array. We will present first spectroscopy results, $^{111}$Nb(p,2p)$^{110}$Zr and $^{112}$Mo(p,3p)$^{110}$Zr cross sections, complementary analysis of neighboring nuclei, implications for structural evolution in the 50$<$N$<$82 region, and the impact on our understanding of the formation of the A=130 r-process peak. Additionally, we report on a broader, ongoing study of (p,2p) and (p,3p) quasi-free scattering cross sections as measured during the SEASTAR (Shell Evolution And Search for Two-plus energies At RIBF) campaigns.

$\gamma$-spectroscopy of neutron-rich $^{79}$Cu through proton knock-out (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Louis Olivier (IPN Orsay)

Room: Scotiabank Theatre Nuclear shell structure is evolving when going into more and more exotic regions. As a consequence, the classical magic numbers, derived from the shell-model in agreement with the experimental knowledge, can be different far from stability. We here discuss about neutron-rich copper isotopes beyond $^{78}$Ni. Different experiments have been performed in the region of $^{78}$Ni at RIKEN, in Japan. During the EURICA campaign where many half-lives have been measured, suggesting $^{78}$Ni to be indeed doubly magic [1]. However, in copper isotopes above $N=40$, a monopole drift has been seen in the past [2,3], leading to the question whether the $Z=28$ shell gap weakens or not when adding neutrons beyond $N=40$. It has been recently observed that this gap is not reduced in $^{71}$Cu ($N=42$) [4]. Further experiments have been performed recently and are analysed at the moment in order to complete the chain of copper isotopes. We shall present the latest results from an experiment leading to selective population of hole states in $^{79}$Cu ($N=50$), through the $^{80}$Zn(p,2p)$^{79}$Cu knock-out reaction, carried out at RIKEN by the SEASTAR collaboration. A $^{238}$U beam, with an energy of 345 MeV/nucleon and an intensity of 15 pnA, was sent on a $^{9}$Be target, creating a cocktail of radioactive isotopes. These isotopes went through the BigRIPS spectrometer, for identification and selection, and reached the liquid-hydrogen target MINOS, where the knock-out reactions took place. The isotopes produced went through the ZeroDegree spectrometer for identification. The DALI2 scintillator array was surrounding MINOS for $\gamma$-ray detection. $\gamma$-$\gamma$ coincidences permitted to build the first level scheme of $^{79}$Cu, with levels up to 4 MeV. Interpretation of this scheme is ongoing, and shell-model calculations are currently being performed by the nuclear theory group of the University of Tokyo. [1] Z. Y. Xu et al., PRL 113, 032505 (2014) [2] S. Franchoo et al., PRL 81, 3100 (1998) [3] K. Flanagan et al., PRL 103, 142501 (2009) [4] P. Morfouace et al., Physics Letters B 751 (2015) 306-310

A high-energy direct reaction study of $^{18}$B and $^{21}$C (Shell evolution through direct reactions)

• Sylvain Leblond (The university of Hong Kong)

Room: Scotiabank Theatre The investigation of the light neutron-rich dripline nuclei, including those exhibiting halos, is a central theme of nuclear structure physics. In the present paper, a study aimed at exploring the structure of the most neutron-rich isotopes of boron and carbon will be presented. Of particular interest are the heaviest candidate two-neutron halo systems, $^{19}$B and $^{22}$C and the associated unbound sub-systems $^{18}$B and $^{21}$C, the states of which are essential to the defining the $^{17}$B-n and $^{20}$C-n interactions for three-body models. In addition, $^{18}$B and $^{21}$C are of much interest in terms of the evolution of shell- structure as their structure can shed light directly on the evolution of the neutron $2s_{1/2}$ and $1d_{5/2}$ single-particle orbitals which are predicted to become degenerate in this region. Motivated by these considerations, we have undertaken an investigation of the structure of $^{18}$B and $^{21}$C using the complementary probes of neutron and proton knockout from high-energy secondary beams provided by the RIKEN RIBF. The experimental setup incorporated the SAMURAI spectrometer coupled to the large area neutron detector NEBULA and the DALI2 NaI array. The results obtained in terms of the invariant mass spectra will presented as will the momentum distributions obtained for the neutron removal. The interpretation in terms of shell-model predictions will be discussed.

Nuclear structure beyond the drip-line: structure of $^9$He and $^{10}$N isotopes (Exotic structures through direct reactions)

• Grigory ROGACHEV (Texas A&M University, College Station, TX, USA)

Room: Scotiabank Theatre Significant progress have been made toward achieving the goal of describing properties of nuclei starting from realistic nucleon-nucleon interactions in the last two decades. The ab initio models were very successful in pushing the limits of their applicability toward nuclear systems with ever more nucleons and exotic neutron to proton ratios. Predictions of these models are often in good agreement with the experimental data, but sometimes deviate from experiment substantially. For example, the exotic isotope of helium, $^9$He, represents a curious case of stark disagreement between the predictions of modern theories and what is believed to be the experimental knowledge for this nucleus. Another interesting exotic system that has been a target of numerous experimental studies is $^{10}$Li. Level structure of this nucleus is still uncertain and presents a major challenge (both theoretically and experimentally). Recent experimental results that shed light on structure of $^9$He and $^{10}$Li will be discussed. The level structure of $^9$He was studied through the T=5/2 isobaric analog states in $^{9}$Li, populated via $^8$He+p resonance scattering [1]. The low-lying levels in $^{10}$N ($^{10}$Li mirror) have been populated in $^9$C+p resonance scattering. Properties of the ground and first excited states of these exotic isotopes will be discussed. [1] E. Uberseder, G.V. Rogachev, V.Z. Goldberg, et al., Phys. Lett. B 754 (2016) 323.

A new study of $^{5}$H (Exotic structures through direct reactions)

• Daniel McNeel (University of Connecticut)

Room: Scotiabank Theatre We have studied the ground state of the extremely neutron-rich isotope of hydrogen, $^{5}$H, using the $^{6}$He(d,$^{3}$He)$^{5}$H reaction in inverse kinematics. Several measurements exist for $^{5}$H (see Ref. [1]), however different results are in conflict with each other and with many theoretical predictions. The present measurement provides a clear evidence for the $^{5}$H ground state, and the previously unreported $^{6}$He(d,t)$^{5}$He ground state reaction is observed in the same experiment. A $^{6}$He beam at 55 AMeV produced at the National Superconducting Cyclotron Laboratory at Michigan State University bombarded a 1.9 mg/cm$^{2}$ (CD$_{2}$)n target. The reaction products were detected with HiRA (the High Resolution Array) [2]. The properties of the $^5$He ground state are well known from neutron scattering and the $^4$He(d,p)$^5$He reaction and provide information about the calibration and response of the apparatus. The $^3$He and $^3$H particles from the $^6$He(d,$^3$He/$^3$H)$^5$H/$^5$He reactions were detected in coincidence with the decay products of the unstable $^5$H and $^5$He nuclei, providing clean signatures for the transitions of interest. The data reveal clear evidence of the $^5$H ground-state resonance at an energy of 2.4±0.4 MeV above the threshold for decay into t+2n, with a width of 4.4±0.4 MeV. Details of the measurement, and a comparison of the results with those of previous measurements and theoretical calculations, will be presented. [1] L. V. Grigorenko, Eur. Phys. J. A 20, 419 (2004) and references therein. [2] M. S. Wallace et al., Nucl. Instrum. and Meth. A 583, 302 (2007).

1-n neutron and 2-protons pick-up reactions to study the unbound nucleus $^7$He (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Francesca Renzi (KU Leuven Department of Physics and Astronomy Instituut voor Kern-en Stralingsfysica)

Room: Scotiabank Theatre The unbound nucleus $^7$He has attracted the interest of several research groups in recent years. However, despite a significant number of experiments, an unambiguous information about $^7$He excited states is still lacking, in particular for the first excited 1/2- state [1-5]. This state is considered the spin-orbit partner of $^7$He ground state. The importance of the spin-orbit interaction in the vicinity of the neutron drip line for shell model calculation highlights the need of additional experimental investigations. In this talk we will report a measurement performed at the LLN facility using a $^6$He beam at 16.8 MeV impinging on a highly pure and self-supporting $^9$Be target. The detection system consisted of two arrays of silicon-strip detectors covering 5-12 degrees and 22-70 degrees in the laboratory system. In these different angular ranges diverse mechanisms may be predominant. Indeed, the $^7$He states can be populated via both 1-neutron ($^6$He,$^7$He) and 2-protons ($^6$He,$^8$Be) transfer reactions. In both cases, thanks to the signature provided by the decay of the outgoing $^8$Be, the decay energy spectrum for $^7$He was obtained via the resonant particle spectroscopy technique. The energy spectrum has been analysed combining an extended Monte Carlo simulation with the R-Matrix theory. This work will present the spectroscopic information obtained from the decay energy spectrum for $^7$He. [1] D. R. Tilley, et al., Nucl. Phys. A 708, 3 (2002) [2] F. Skaza, et al., Phys. Rev. C 73, 044301 (2006) [3] G.V. Rogachev, et al., Phys. Rev. Lett. 92, 23 (2004) [4] N. Ryezayeva, et al., Phys. Lett. B 639, 623 (2006) [5] A.H. Wuosmaa, et al., Phys. Rev. C 78, 041302 (2008)

Nuclear structure study for the neutron-rich nuclei beyond $^{132}$Sn (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• He Wang (RIKEN Nishina Center)

Room: Scotiabank Theatre The properties of the nuclei with a few valence particles and/or holes outside of a doubly magic nucleus are essential in the fundamental understanding of nuclear physics. In particular, the exotic nuclei around $^{132}$Sn have received much attention because $^{132}$Sn is doubly magic while lying far away from the line of $\beta$ stability. It thus provide a pivotal area to explore the possible modification in the nuclear structure towards the neutron-drip line. However, the experimental knowledge on the spectroscopic information for the nuclei located beyond $^{132}$Sn is very limited because of the difficulty in access to this region experimentally. Aiming at investigating the possible structural changes in this region, we have studied the first $2^+$ ($2_1^+$) states in the neutron-rich nuclei $^{136}$Sn and $^{132}$Cd at the RI Beam Factory. The observed $2_1^+$ state in $^{132}$Cd provides the first spectroscopic information southeast of $^{132}$Sn. One experimental challenge is the difficulty in the access to these two exotic nuclei. This experiment employed one- and two-proton removal reactions following the in-flight fission of primary U beam to produce $^{136}$Sn and $^{132}$Cd. The $2_1^+$ states in $^{136}$Sn and $^{132}$Cd were identified by measuring $\gamma$ rays in coincidence with these reactions. The secondary beams were produced in the BigRIPS separator and the reaction residues were analyzed by the ZeroDegree spectrometer. Gamma rays emitted from the excited states were measured via the DALI2 spectrometer. In the presentation, the new results on the $2_1^+$ states in $^{136}$Sn and $^{132}$Cd will be discussed and experimental details will be given.

Inclusive deuteron-induced reactions

• Gregory Potel Aguilar (Michigan State University)

Room: Scotiabank Theatre Deuteron-induced reactions have long been used to probe single-particle aspects of nuclear spectra. Understanding the reaction mechanism is essential in order to disentangle direct reaction contributions (transfer and elastic breakup) from compound nucleus formation and partial or total fusion. Furthermore, as one moves away from the Fermi energy, such states acquire a larger width, and, while approaching the drip line, the Fermi energy eventually slides into the continuum. Aside from providing valuable spectroscopic information, (d,p) reactions in which the neutron is absorbed by the heavy nucleus can be used as surrogates for (n,gamma) reactions, of great practical and astrophysical interest. We thus present a formalism able to deal with the variety of processes (direct transfer to sharp states, transfer to wide states, population of resonances in the continuum, capture, elastic breakup, etc.) encountered in the context of a (d,p) process.

Towards an ab initio description of nuclear radiative captures (Theoretical developments of direct reactions)

• Jérémy Dohet-Eraly (TRIUMF)

Room: Scotiabank Theatre The recent progresses in the development of ab initio approaches makes possible the description of bound and scattering states for light nuclear systems in a unified framework, based on microscopic Hamiltonians built within chiral effective theory. Among these approaches, the No-Core Shell Model with Continuum (NCSMC) [1,2] has been proved to be particularly successful for studying resonances and elastic scattering for five- and six-nucleon systems [3,4]. The extension of this approach to the description of electromagnetic transitions in nuclear systems will be presented. This provides an interesting tool to probe the quality of the ab initio wave functions and thus of the chiral inter-nucleon interactions. I will present the application of the NCSMC approach to the radiative capture processes, in particular, to the astrophysically important $^3$He(α,γ)$^7$Be and $^3$H(α,γ)$^7$Li reactions [5]. Both reactions are essential to calculate the primordial $^7$Li abundance in the universe. Moreover, the $^3$He(α,γ)$^7$Be capture is one of the key reactions to understand the solar neutrino flux, along with the $^7$Be(p,γ)$^8$B reaction. If time allows, the $^7$Be(p,γ)$^8$B reaction will be also considered. [1] S. Baroni, P. Navrátil, S. Quaglioni, Phys. Rev. Lett. 110, 022505 (2013). [2] S. Baroni, P. Navrátil, S. Quaglioni, Phys. Rev. C 87, 034326 (2013). [3] G. Hupin, S. Quaglioni, P. Navrátil, Phys. Rev. C 90 (2014) 061601(R). [4] G. Hupin, S. Quaglioni, P. Navrátil, Phys. Rev. Lett. 114 (2015) 212502. [5] J. Dohet-Eraly et al., arXiv:1510.07717 [nucl-th].

Tetraneutron states populated by $^4$He($^8$He,$^8$Be) reaction (Probing the nuclear force through direct reactions)

• Susumu Shimoura (Center for Nuclear Study, University of Tokyo)

Room: Scotiabank Theatre We have found a candidate tetraneutron resonant state via a double-charge exchange (DCX) reaction $^4$He($^8$He,$^8$Be) at 190 $A$ MeV by using the SHARAQ spectrometer at the RIBF facility in RIKEN$^{1)}$. Production mechanism with kinematical consideration for the present exotic reaction is introduced and analysis for obtaining missing-mass spectrum is presented. The observed missing-mass spectrum consists of a continuum consistent with a prediction assuming direct decay from a wave packet produced just after the DCX reaction and a peak just above the 4n threshold. The energy of the peak is 0.83$\pm$0.65(stat.)$\pm$1.25(syst.) MeV with a significance level of 4.9$\sigma$, which is a candidate of a tetraneutron resonance. Three-body forces relevant for formation of tetraneutron resonance are discussed for consistent understanding of few-body systems. Further experimental approaches for the tetra-neutron system at the RIBF are also shown. [1] K. Kisamori et al., Phys. Rev. Lett. **116**, 052501 (2016)

Pairing rotations in ground states of open-shell even-even deformed nuclei (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Nobuo Hinohara (University of Tsukuba / Michigan State University)

Room: Scotiabank Theatre A pairing rotation, which has been seen in binding energies of open-shell semi-magic nuclei, such as Sn and Pb isotopes, is a signature of nuclear superconductivity; it explains the collective enhancement of two-nucleon transfer cross sections between ground states of even-even nuclei [1]. By applying the linear response formalism to the zero-energy Nambu-Goldstone pairing mode within the nuclear energy density functional theory [2], we compute the pairing-rotational moments of inertia in open-shell nuclei, and show that the state-of-the-art nuclear energy density functional [3,4] reproduces the experimental binding energy differences in the semi-magic systems such as Ca, Ni, Sn, and Pb isotopes, and N=50, 82 isotones. We extend our analysis to open-shell deformed nuclei, with both of the neutrons and protons being in the superconducting phases, and show how the mixing of neutron and proton pairing rotational modes can explain the experimental double binding-energy differences [5]. Our results confirm that the symmetry-restoring pairing rotational modes are tilted in the neutron-proton two-dimensional gauge space due to the residual neutron-proton interaction. These findings emphasize the importance of pairing rotational modes for two-nucleon and, possibly, alpha transfer reactions between the ground states of even-even open-shell nuclei. References: [1] G. Potel, F. Barranco, F. Marini, A. Idini, E. Vigezzi, and R.A. Broglia, Phys. Rev. Lett. 107, 092501 (2011); 108, 069904 (2012). [2] N. Hinohara, Phys. Rev. C 92, 034321 (2015). [3] S. Bogner et al., Comput. Phys. Commun. 184, 2235 (2013). [4] N. Schunck et al., J. Phys. G: Nucl. Part. Phys. 42, 034024 (2015). [5] N. Hinohara and W. Nazarewicz, arXiv:1601.00677.

Neutron-proton pairing in the self-conjugate unstable nuclei $^{56}$Ni and $^{52}$Fe through transfer reactions (Probing the nuclear force through direct reactions)

• Marlène Assié (IPN)

Room: Scotiabank Theatre Neutron-proton pairing is the only pairing that can occur in the T=0 and the T=1 isospin channels. T=1 particle-like pairing (n-n or p-p) has been extensively studied unlike T=0 neutron-proton pairing. The over-binding of N=Z nuclei could be one of its manifestation. Neutron-proton pairing can be studied by spectroscopy as in ref.[1].We have studied it through transfer reactions in order to get more insight into the relative intensities of the two aforementioned channels. Indeed, the cross-section of np pair transfer is expected to be enhanced if the number of pairs contributing to the populated channel is important. Neutron-proton pairing is predicted to be more important in N=Z nuclei with high J orbitals so that the best nuclei would belong to the g9/2 shell [2]. However, considering the beam intensities in this region, we have focussed on fp shell nuclei ($^{56}$Ni and $^{52}$Fe). The measurement was performed at GANIL with radioactive beams produced by fragmentation of a 75A MeV $^{58}$Ni beam on a 185 mg.cm-2 Be target purified by the LISE spectrometer. An efficient set-up based on the coupling of the MUST2 and TIARA Silicon arrays for charged particle detection with the EXOGAM gamma-ray detector was used. Measuring both $^{52}$Fe (N=Z=26) which is a partially occupied 0f7/2 shell nucleus and $^{56}$Ni (N=Z=28) which has a fully occupied 0f7/2 shell will allow us to study np pairing according to shell occupancy. First results on the nature of the n-p pairing will be discussed based on the relative intensities of the 0+ and 1+ states populated in the $^{56}$Ni(p,$^3$He)$^{54}$Co and $^{52}$Fe(p,$^3$He)$^{50}$Mn reactions and on the angular distributions compared with DWBA calculations. [1] B. Cederwall et al, Nature 469 (2011) 469. [2] P. van Isäcker et al, Phys. Rev. Lett. 94 (2005) 162502.

Systematic study of neutron-proton pairing in {\it sd}-shell nuclei via (p,$^{3}$He) and ($^{3}$He,p) transfer reactions (Probing the nuclear force through direct reactions)

• Yassid Ayyad (National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.)

Room: Scotiabank Theatre The transfer of a neutron-proton pair from even-even to odd-odd self-conjugate nuclei stands out as the best tool to investigate np correlations being (p,$^{3}$He) and ($^{3}$He,p) the reaction of choice with high sensitivity. The exclusive cross sections populating to the lowest $J^{\Pi}=0^{+}, 1^{+}$ states in the odd-odd $N=Z$ nuclei and the corresponding $\sigma(J^{\Pi}=0^{+})/\sigma(J^{\Pi}=1^{+})$ provide a model-independent approach to quantify the nature and interplay between $T$=0 ($J$=1) and $T$=1 ($J$=0) pairing correlations. Nevertheless, the existing data concerning the $\sigma(J^{\Pi}=0^{+})/\sigma(J^{\Pi}=1^{+})$ ratio present clear inconsistencies in the trends across the sd-shell. These problems may be associated to the fact that the measurements were performed in different experimental conditions. Moreover, for some of the previous data no cross sections were obtained at forward angles and even in some of these measurements the absolute cross sections were not determined. In order to shed light to these discrepancies, we conducted an experiment at Research Center for Nuclear Physics (RCNP - Osaka University) to perform a series of systematic measurements of ($p$,$^{3}$He) and ($^{3}$He,$p$) on $^{24}$Mg, $^{32}$S, $^{28}$Si and $^{40}$Ca targets. In addition, the joint analysis of the proposed systematic measurements will help to complete the understanding of using both np-pair stripping and pickup transfer mechanism for probing np pairing correlations. The systematics data sets are compared with predictions from the reaction framework coupled with structure model to evaluate the microscopic description of np pairing correlations in this region.

Parity-transfer ($^{16}$O,$^{16}$F(0$^-$)) reaction for study of spin-dipole 0$^-$ mode (Exotic structures through direct reactions)

• Masanori Dozono (Center for Nuclear Study, University of Tokyo)

Room: Scotiabank Theatre The spin-dipole (SD) $0^-$ excitation characterized by $\Delta L=1$, $\Delta S=1$, and $\Delta J^{\pi}=0^-$, attracts recent theoretical attention due to its strong relevances to the tensor correlations in nuclei. For example, self-consistent HF+RPA calculations in Ref. [1] predict that the tensor correlations produce a strong hardening (shifting toward higher excitation energy) effect on the $0^-$ resonance. It is also predicted that the effect is sensitive to the magnitude of the tensor strength. Thus experimental data of the SD $0^-$ distribution enable us to quantitatively examine the tensor correlation effects. Despite this importance, experimental information on $0^-$ states is limited because of the lack of the experimental tools that are suitable for the $0^-$ studies. We propose a new probe, the parity-transfer $(^{16}{\rm O},^{16}{\rm F}(0^-,{\rm g.s.}))$ reaction, for the $0^-$ studies [2]. The parity-transfer reaction uses $0^+ \rightarrow 0^-$ transition in the projectile to probe $0^-$ states in a target nucleus. This reaction has a unique selectivity to unnatural-parity states, which is an advantage over the other reactions used so far. The first experiment for a ${}^{12}{\rm C}$ target was performed at the RIKEN RI Beam Factory by using the SHARAQ spectrometer [3]. In this presentation, we will report the details of the experiment and the results. [1] H. Sagawa, G. Coló, Prog. Part. Nucl. Phys., 76 (2014) 76 [2] M. Dozono et al., RIKEN Accel. Prog. Rep., 45 (2012) 10 [3] T. Uesaka et al., Prog. Theor. Exp. Phys., 2012 (2012) 03C007

Two-neutron transfer reactions as a probe of isospin mixing effects in superallowed beta decay (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Kyle Leach (Colorado School of Mines)

Room: Scotiabank Theatre As part of an ongoing program to study fundamental symmetries in nuclear physics, superallowed Fermi $0^+\rightarrow0^+$ $\beta$ decay provides by far the most precise determination of the vector coupling constant for the weak interaction, $G_V$. Currently, the precision on the extraction of this quantity from the superallowed data is limited by theoretical corrections that must be applied. These corrections are difficult to calculate, and those that rely on nuclear-structure theory require benchmarking to experimental data. Of particular interest to the isospin-symmetry-breaking (ISB) portion of these theoretical corrections is the degree to which isospin mixing occurs between the isobaric analogue state and other excited $0^+$ states. These measurements are particularly difficult for intermediate-mass nuclei, where the superallowed $\beta$ decay $Q$-value windows are very large, and $0^+$ states with very low reaction cross-sections (~few $\mu$b/sr) must be mapped to several MeV. Our recent two-neutron transfer work on both the $A=62$ and $A=50$ superallowed systems have shown discrepancies in both the number and energy of previously assigned $0^+$ states, thus impacting the magnitude of the currently adopted ISB corrections for these nuclei. These results will be presented, as well as implications of this work for the extraction of $G_V$ from the superallowed data.

Advances in explosive nuclear astrophysics using radioactive beams

• Gavin Lotay (University of Surrey)

Room: Scotiabank Theatre Breathtaking results from the Planck satellite mission and Hubble space telescope have highlighted the key role modern Astronomy is playing for our understanding of Big Bang Cosmology. However, not so widely publicized is the similar wealth of observation data now available on explosive stellar phenomena, such as X-ray bursts, novae and Supernovae. These astronomical events are responsible for the synthesis of almost all the chemical elements we find on Earth and observe in our Galaxy, as well as energy generation throughout the cosmos. Regrettably, understanding the latest collection of observational data is severely hindered by the current, large uncertainties in the underlying nuclear physics processes that drive such stellar scenarios. In order to resolve this issue, it is becoming increasingly clear that there is a need to explore the unknown properties and reactions of nuclei away from the line of stability. Consequently, state-of-the-art radioactive beam facilities have become terrestrial laboratories for the reproduction of explosive astrophysical events. In this talk, both direct and indirect methods for studying key astrophysical reactions using radioactive beams will be discussed.

Study of the resonance state(s) in $^{20}$Mg: astrophysical implications and understanding the nuclear forces (Nuclear astrophysics)

• Jaspreet Randhawa (Saint Mary's University, Halifax)

Room: Scotiabank Theatre Study of proton unbound resonance states in $^{20}$Mg is important for both nuclear structure and nuclear astrophysics. Type-I X-ray bursts in accreting neutron stars are triggered by the break out reactions from hot CNO cycles. In one of the break out sequences $^{18}$Ne is a waiting point as it cannot undergo proton capture because that leads to proton unbound $^{19}$Na, So it has to wait for beta decay to happen. $^{18}$Ne(2p,$\gamma$)$^{20}$Mg has been suggested as one of the possible bypass path to rp-process nucleosynthesis. The resonant states above the proton emission threshold in $^{20}$Mg determine the $^{18}$Ne(2p,$\gamma$)$^{20}$Mg resonant capture reaction rate. Due to the lack of experimental data, reaction rate estimates for this reaction are currently based on the energy levels of $^{20}$O taken from shell model predictions (Gorres et al.,1995). Recent calculations using nuclear forces from chiral perturbation theory predict quite a different level structure for $^{20}$Mg using the nucleon-nucleon (NN) force only and nucleon-nucleon plus three nucleon (NN+3N) forces (Holt et al.,2013). These predictions are also different from the levels predicted by shell model calculations and assuming mirror symmetry to $^{20}$O. This makes the study of the excited states of $^{20}$Mg important. In this presentaion we will report the investigation of the excited states in $^{20}$Mg through $^{20}$Mg(d,d')$^{20}$Mg* inelastic scattering. The experiment was performed using the IRIS facility, stationed at TRIUMF, Canada. The $^{20}$Mg beam with an average intensity of ~500 pps was post accelerated to an energy of 8.5A MeV. The speciality of IRIS is the use of a thin windowless solid deuteron target which makes this study possible with such a low beam intensities.

Study of the $^{30}$P(d,n)$^{31}$S reaction to probe astrophysical resonance strengths (Theoretical developments of direct reactions)

• Terri Poxon-Pearson (National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University)

Room: Scotiabank Theatre The $^{30}$P(p,$\gamma$)$^{31}$S proton capture reaction is a bottleneck for nucleosynthesis towards heavier nuclei during nova outbursts. This reaction is inaccessible experimentally in the relevant energy region, but its reaction rate can be probed using the $^{30}$P(d,n)$^{31}$S transfer reaction. By determining the energies and spin assignments of low lying states in $^{31}$S populated by this transfer reaction, one can recover the resonance strength for the desired $^{30}$P(p,$\gamma$)$^{31}$S proton capture. This resonance strength is a key component of determining the reaction rate at astrophysical temperatures. There is, however, wide disagreement regarding spin assignments for these resonance states, including recent shell model calculations which indicate negative parity states should dominate the reaction rate in the Gamow window [1]. The $^{30}$P(d,n)$^{31}$S experiment was carried out at the National Superconducting Cyclotron Laboratory at Michigan State University, where a radioactive beam of $^{30}$P with E=30 MeV/u impinged on a thick, deuterated target. The resonances were identified by their $\gamma$ decays with the high resolution GRETINA detector. These gamma decays were measured in coincidence with $^{31}$S detections in the S800 Spectrograph. This method allows for high energy resolution and angle-integrated cross sections, which can be compared to reaction theory predictions. This new method has been successfully employed to analyze the $^{26}$Al(d,n)$^{27}$Si reaction. Comparison to theoretical calculations for this reaction reached good agreement and resonance strengths were extracted for the astrophysically relevant $^{26}$Al(p,$\gamma$)$^{27}$Si reaction [2]. This indicates that it is a reliable method for estimating resonance strengths for similar reactions. For the $^{30}$P(d,n)$^{31}$S reactions we calculated total cross sections using the framework of the Adiabatic Distorted Wave Approximation (ADWA) which explicitly takes deuteron breakup into account to all orders [3]. The calculations were done using TWOFNR [4] and FRESCO [5]. The theoretical (d,n) cross sections can be used in the analysis of the data to produce experimental spectroscopic factors. Reaction calculations for similar systems with low lying resonances have used a bound state approximation which artificially binds the resonant state by a few eV, but the accuracy of this approximation had not been tested rigorously. During our investigation we explored the limits of this approximation and discovered that the approximation was not valid for some cases, yielding percent differences of more than 10% for states of $^{31}$S with low angular momentum. When our approximation did not hold, we introduced a resonance at the experimental energy and constructed a bin wave function to account for these states. Another source of uncertainty in these calculations is the optical potential, in this case neutrons on $^{30}$P, protons on $^{30}$P, and protons on $^{31}$S. The optical potentials we use are derived from fits to stable target data sets at different energies and mass number and then extrapolated. We make different choices for the optical potentials used in our calcutions to gauge the uncertainty in the calculated cross sections. [1] B. Alex Brown, W.A.Richter, and C. Wrede, Phys. Rev. C 89, 062801 June, 2014. [2] A. Kankainen et al, Eur. Phys. J. A 52 Jan, 2016. [3] R.C.Johnson, P.C. Tandy, Nucl. Phys. A 235, 56 (1974). [4] M.T.J Tostevin, M. Igarashi, N. Kishida, University of Surrey modified version of the code TWOFNR, private communication. [5] I. Thompson, Comput. Phys. Rep 7, 167 (1988).

Nuclear structure at the limits relevant to nuclear astrophysics (Nuclear astrophysics)

• Lidia S. Ferreira (CeFEMA/IST/UNIV Lisbon, Portugal)

Room: Scotiabank Theatre L.S. Ferreira* and E. Maglione† *Center of Physics and Engineering of Advanced Materials, CeFEMA and Departamento de Física, Instituto Superior Técnico, Universidade de Lisboa, Avenida Rovisco Pais, P1049-001 Lisbon, Portugal †Dipartimento di Fisica e Astronomia “G. Galilei”, Via Marzolo 8, I-35131 and Istituto Nazionale di Fisica Nucleare, Padova, Italy Nuclear structure far from stability plays a crucial role in the formation of heavy elements, during stellar evolution. In explosive scenarios, the density and temperature are so high, that rapid proton capture can occur, generating unstable nuclei up to the proton drip-line. Starting as a break out of the hot CNO cycle, and through many possible paths all proton rich nuclei up to the Sn region are generated, from p capture or photo disintegration of some seed nuclei, but there are many uncertainties about their origin, since most of these reactions proceed through resonances, in very unstable drip-line nuclei. In this region, the proton drip line also evolves almost along the N=Z line, relevant for the study of fundamental symmetries. Therefore, the experimental and theoretical study of radioactive proton capture (p,γ) reactions in light and intermediate nuclei, are an important input to nucleosynthesis scenarios, along with the identification of the resonances, and their parameters which highly influence the reaction rates, However, direct measurements on unstable nuclei are still a major challenge in nuclear physics. At the proton drip line, the observation and theoretical interpretation of proton emission has been the only possibility to access the nuclear structure properties in this region[1,2]. Since the emission of a proton from an excited state is just the inverse of the (p,γ) reaction, the information obtained from the interpretation of decay and structure properties of theses nuclei far from stability, can help to constraint astrophysical models. An example of this procedure was given by our analysis of sequential two proton emission from $^{18}$Ne[3]. We were able to identify very narrow high energy states of negative parity in $^{18}$Ne, which prefer to decay by one proton emission to the excited states of the daughter $^{17}$F, than to the ground state, thus becoming possible candidates for the emission of a second proton in the sequential decay process. Some of these resonances have been confirmed in experimental studies[4]. Decay to Fluorine is just the inverse of $^{17}$F(p,γ)$^{18}$Ne, very important within the context described above. With most recent developments in production and detection techniques[5], new proton emitters are being produced and their spectrum was also observed, along with the γ´s from some electromagnetic transitions. It is the purpose of this talk to discuss other exotic nuclei in the region N~Z ~30, relevant in the nuclear astrophysics, and for the study of fundamental symmetries, where from the interpretation of their decay data by proton emission, one can identify properties of their spectra and shape. [1] L. S. Ferreira, E. Maglione, P. Ring, Phys Lett. B753 (2016) 237; P. Arumugam, L. S. Ferreira, E. Maglione, Phys. Lett. B680 (2009) 443. [2] M.G.Procter, et al, Physics Letters, B725 (2013) 79. [3] L. S. Ferreira, Journal of Phys. 580 (2015) 012034. [4] G. Raciti et al, Phys. Rev. Lett. 100 (2008) 192503. [5] M.Taylor, et al. Phys. Rev. C 91 (2015) 044322.

Measurement of the $^{26}$Al(d,p) reaction to constrain the $^{26}$Al(p,gamma) rate at stellar temperatures (Nuclear astrophysics)

• Steven Pain (ORNL)

Room: Scotiabank Theatre The long-lived radioactive nuclide $^{26}$Al is a predominant target for γ-ray astronomy, including the first all-sky survey of an individual γ-ray line. Massive stars have been highlighted as a dominant source of ongoing synthesis of $^{26}$Al [1]. At these stellar temperatures, the $^{26}$Al(p,γ)27Si reaction is expected to be the main reaction destroying $^{26}$Al, thus impacting the net $^{26}$Al production [2]. However, the strengths of low-lying resonances in $^{27}$Si wihch determine this rate are not well-constrained experimentally, and are the subject of recently renewed interest [3]. In order to determine spectroscopic information for the mirror states to astrophysically-important resonances in $^{27}$Si, and thereby constrain the reaction rate via these resonances, the $^{26}$Al(d,p)$^{27}$Al reaction has been measured [4]. The experiment was performed at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory, using a beam of ~5 million $^{26}$Al per second. The SIDAR and ORRUBA silicon detector arrays were used to measure proton ejectiles backwards of 90 degrees in the laboratory. Spectroscopic information was determined for mirrors to the astrophysically-relevant resonances, which were found to differ significantly from previously adpoted values. Details of the astrophysical motivation, experiment, and results will be presented. Work supported in part by the US Department of Energy and the National Science Foundation [1] J. Knödlseder, Astrophys. Lett. Commun. 38, 379 (1999) [2] C. Iliadis, A. Champagne, A. Chieffi, and M. Limongi, Astrophys. J. Suppl. Ser. 193, 16 (2011) [3] A. Parikh, J. José, A. Karakas, C. Ruiz, and K. Wimmer, Phys. Rev. C 90 038801 (2014) [4] S.D. Pain et al., Phys. Rev. Lett. 114, 212501 (2015)

Identification of multiple neutrons with MoNA

• Anthony Kuchera (National Superconducting Cyclotron Laboratory)

Room: Scotiabank Theatre The Modular Neutron Array (MoNA) has been used extensively to study neutron-unbound nuclei with invariant mass spectroscopy. The measurements have extended to nuclei which have two neutrons beyond the drip-line including $^{10}$He, $^{13}$Li, $^{16}$Be, and $^{26}$O. Two-neutron emitters have multiple mechanisms in which they can decay. The decay mode can be determined by the three-body correlations. A recent experiment at the NSCL populated excited states in $^{24}$O through inelastic excitation on a liquid deuterium target. A state with excitation energy of 7.65 MeV was observed to decay sequentially through an intermediate state in $^{23}$O before decaying to the ground state of $^{22}$O. This result shows the first observation of two-neutron sequential decay, determined by angular and energy correlations, in the $^{22}$O+2n system. The next challenge is to identify decays by three and four neutrons. Recent work has taken the first steps for the MoNA collaboration in identifying decays by more than two neutrons. An analysis of two-proton removal from a $^{17}$C beam searched for resonances in $^{15}$Be which could decay sequentially through $^{14}$Be to $^{12}$Be. It was found that a new state was not required to fit the data, however, limits on the strength and decay energy of a new state were determined. Details on these and other recent results will be presented.

Experimental study of the knockout reaction mechanism using $^{14}$O at 60 MeV/nucleon (Exotic structures through direct reactions)

• Yelei Sun (The University of Hong Kong)

Room: Scotiabank Theatre Knockout reactions, together with the associated reaction models for deducing spectroscopic factors are the powerful tool to probe the single-particle structure and nucleon correlation in exotic nuclei. For the deeply-bound nucleon removal using C or Be target, a strong reduction in the spectroscopic factor deduced using Glauber-based reaction model from experiment relative to the shell-model calculations is found [1]. Such large disagreement has not been explained and is inconsistent with results from systematic studies of transfer reactions [2,3]. The recently observed asymmetric parallel momentum distribution of the knockout residue indicates the significant dissipative core-target interaction in the knockout reaction with a composite target [4]. To investigate the one-nucleon knockout mechanism, we have performed the fully exclusive measurement of $^{14}$O using $^{12}$C target at 60 MeV/nucleon at RCNP in Osaka University. Coincidence measurement of the knockout residues and the associated decay protons was achieved, which allows us to probe the core-excitation strength quantitatively via the invariant mass method. The upper limits of the cross section for one-neutron removal from $^{14}$O followed by proton evaporation is obtained. The data provide the first constraint on the role of core excitation and evaporation processes in the deeply-bound nucleon removal from very asymmetric nuclei. The experimental results are consistent with the prediction of Intra-nuclear Cascade (INC), shedding light on the long-standing intriguing puzzle of the discrepancy between measurements and eikonal-model predictions for knockout reaction. In this talk, the experimental setup and the physics results will be discussed. [1] A. Gade et al., Phys. Rev. Lett. 93, 042501 (2004). [2] J. Lee et al., Phys. Rev. Lett. 104, 112701 (2010). [3] F. Flavigny et al., Phys. Rev. Lett. 110, 122503 (2013). [4] F. Flavigny et al., Phys. Rev. Lett. 108, 252501 (2012).

Interaction cross section measurements of neutron-rich nuclei $^{17,19}$B (Exotic structures through direct reactions)

• Atsumi Saito (Tokyo Institute of Technology)

Room: Scotiabank Theatre We measured the interaction cross sections of ¹⁷B and ¹⁹B on a carbon target by the transmission method at 270MeV/nucleon and 220 MeV/nucleon, respectively, using SAMURAI facility commissioned in 2012 at RIKEN RI beam factory (RIBF). The drip-line nucleus ¹⁹B has attracted much attention because of its small two neutron separation energy (*S_2n*=0.14(39) MeV [1]) and the large matter radius (r ̃_m=3.11(11) fm) deduced from the measured interaction cross section (σ_I=1219 (81) mb) at an incident energy of 740 MeV/nucleon [2]. These results suggest a neutron halo structure, however its microscopic structure has not yet been well understood. For ¹⁷B, the narrow longitudinal momentum distribution of ¹⁵B from the breakup of ¹⁷B suggested a halo structure of ¹⁷B [3]. Aiming at clarifying the detailed nuclear structures of ¹⁷B and ¹⁹B, we measured the interaction cross sections of these nuclei at different incident energies from the previous experiment. Owing to the high secondary beam intensity at the RIBF, interaction cross sections of these nuclei with a higher accuracy, compared with the previous measurement was obtained. The experimental cross sections are compared with the Glauber model theory using a density distribution obtained from a Hartree- Fock calculation. In the presentation, valence neutron configurations and neutron separation energies of these nuclei will be discussed. [1] L. Gaudefroy et al.: Phys. Rev. Lett. 109 (2012) 202503 [2] T. Suzuki et al.: Nucl. Phys. A 658 (1999) 313-326 [3] T.Suzuki et al.: Phys. Rev. Lett. 89 (2002) 12501

Quasi-free proton knockout reactions on oxygen isotopic chain (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Leyla Atar (TU Darmstadt, Germany)

Room: Scotiabank Theatre According to the Independent Particle Model (IPM) single-particle states are fully occupied with a spectroscopic factor one. However in electron-induced proton knockout reactions a reduction of single-particle strengths has been observed to about 60-70% for stable nuclei in comparison to the IPM [1]. This finding has been confirmed by nuclear knockout reactions using stable and exotic beams, however, with a strong dependency on the proton-neutron asymmetry [2], which is not yet well understood. To understand this dependency quantitatively a complementary approach, quasi-free reactions, is introduced. Quasi-free knockout reactions in inverse kinematics at relativistic energies provide a direct way to investigate single-particle structure of stable and exotic nuclei [3]. We have performed a systematic study of spectroscopic strength of oxygen isotopes using quasi-free (p,2p) knockout reactions in complete kinematic at the R3B/LAND experimental setup (at GSI in Darmstadt, Germany) with secondary beams containing $^{13−24}$O. The oxygen isotopic chain offers a large variation of separation energies, which allow us to obtain a quantitative understanding of spectroscopic factors with respect to isospin asymmetry. We will present systematic results on the entire oxygen isotopic chain obtained in a single experiment. The results include total and partial cross sections extracted by means of gamma-coincidence measurements as well as momentum distributions. The latter is sensitive to the angular momentum of the knocked-out nucleon in the projectile. By comparison with the eikonal reaction theory [4] the spectroscopic factors and reduction factors as a function of separation energy have been extracted and will be compared to existing data in literature. The work is supported by HIC for FAIR, GSI-TU Darmstadt cooperation, and BMBF project 05P15RDFN1. 1. L. Lapikas Nucl. Phys. A553, 297c (1993). 2. J. A. Tostevin, A. Gade Phys. Rev. C 90, 057602 (2014). 3. V. Panin et al. Phys. Letters B 753, 204-210 (2016). 4. T. Aumann, C. Bertulani, J. Ryckebusch Phsy. Rev. C 88, 064610 (2013).

Two-neutron halo of drip-line nuclei from the low-energy limit of neutron-neutron interaction (Exotic structures through direct reactions)

• Toshio Suzuki (Department of Physics, College of Humanities and Sciences, Nihon University)

Room: Scotiabank Theatre The formation of two-neutron halo is described using the neutron-neutron ($nn$) interaction fixed at the low-energy $nn$ scattering limit [1]. This method is tested for loosely-bound two neutrons in $^{24}$O, where a good agreement with experimental data is found. It is applied to halo neutrons in $^{22}$C in two ways: with the $^{20}$C core being closed or correlated due to excitations from the closed core. This $nn$ interaction is shown to be strong enough to produce a two-neutron halo in both cases, locating $^{22}$C on the drip line, while $^{21}$C remains unbound. A unique relation between the two neutron separation energy, $S_{2n}$ and the radius of neutron halo is presented. New predictions for $S_{2n}$ and the radius of neutron halo are given for $^{22}$C. The appearance of Efimov states is also discussed. Spectra of excited states in $^{22}$C are predicted. [1] T. Suzuki, T. Otsuka, C. Yuan and N. Alahari, Phys. Lett. B 753, 199 (2016).

Direct reactions with weakly-bound systems: a one-dimensional model (Theoretical developments of direct reactions)

• Laura Moschini (Padova University - INFN Padova - Sevilla University)

Room: Scotiabank Theatre In this contribution we develop a simple model aiming at the description of the structural and dynamical properties of weakly-bound systems with one or more valence particles. Even considering inert cores, the description of these systems is relatively easy in the case of one valence particle (one-particle halo), but starts to be more complex with two particles (two-particle halo), becoming extremely complicated for systems with more active particles. For these reasons one typically resorts to approximate schemes (coupled-channels, first-order approximation, space truncation, effective optical potentials and form factors, continuum discretization, etc) that need to be tested, not only against experimental data. $~~~$The main purpose of this work is precisely the comparison between approximate models and exact ones. However, mathematical complexities and the required high computational power constitute a huge difficulty for obtaining the exact results. Therefore, to make feasible the exact solution of the problem, particles are assumed to move just in a one dimension and the colliding nuclei to move according to classical trajectories. In spite of these drastic assumptions, we are confident that the problem retains the main features and properties of the full three-dimensional case. The model will allow us to shed some light on the reaction mechanism, namely on the description of the process in terms of single or repeated action of the external field in a perturbative expansion. A typical example is provided by the long-standing problem of the two-particle transfer process, which is described either as a pair transfer in a single shot or as a correlated sequence of single-particle transfers through a number of intermediate states. $~~~$In the case of one particle, the active neutron is initially sitting on a single-particle level of a one-body Woods-Saxon potential and feels the action of a second moving potential. The target potential is assumed to be at rest in a fixed position, whereas the projectile moves following a fixed classical trajectory. The choice of the parameters entering in the calculation will lead to various structural and kinematical conditions, corresponding to rather different physical situations and simulating different bombarding energy regimes, impact parameters, and Q-values for particle transfer. Essentially, one has to fix the parameters characterizing the potential wells (energies of single-particle states in both potentials), initial condition (selecting one of the single-particle levels in target potential), distance of closest approach, and asymptotic energy of the collision. The ``exact'' result is obtained by solving numerically the time-dependent one-particle Schroedinger equation. The probability for populating the different channels (elastic, inelastic, transfer, and breakup) after the collision is determined by projecting the asymptotic wave function (i.e.\ the solution for large values of t) onto the corresponding eigenstates of the wells. The same problem is then solved within the first order approximation or standard coupled-channels formalism, thus testing the validity of the necessary truncations and continuum discretization. In particular, by this comparison, one might infer the importance of including the continuum in the coupled-channels calculation. $~~~$We extended the model to the case of two valence neutrons. As in previous case, the initial two-particle state is generated by the fixed well and the time evolution of the two-particle wave function is due to the action of the second moving potential along a classical trajectory. In addition, one includes a residual zero-range pairing interaction between the two valence particles that, for simplicity, is taken to be density-dependent. Again, the system evolution is obtained by solving numerically the time-dependent Schroedinger equation for the two-particle wave function. At the end of the process one can project out the population of the different final channels: elastic/inelastic (both particles still in the initial well), one-particle transfer (one particle in the initial well and one in the moving one), one-particle breakup (one particle in the continuum outside the wells and one in the initial or final well), two-particle transfer (both particles in the moving well), and two-particle breakup (both particles outside the wells). We can study the reaction mechanism by switching on or off the pairing interaction. In the case in which the pairing interaction is switched off (uncorrelated case), the two-particle transfer process can only be interpreted as produced by the successive transfer of single particles generated by the moving one-body field, and in fact the value obtained agrees with the one obtained in a perturbative two-step approach. In the case with correlations the initial wave function is obtained by diagonalizing the residual pairing interaction in the two-particle basis, and the effect of this initial correlation will propagate during the scattering process. As a result, although the transfer is still induced by the moving one-body field, we find a final probability for pair transfer larger than the uncorrelated estimate. This increase represents therefore the enhancement factor due to the pairing correlation. $~~~$In conclusion, despite its simplicity, the model provides a framework for the clarification of different aspects of direct reactions involving one- and two-particle halo nuclei. In particular it permits to test in a simple way the role of continuum within the usual approximate approaches and to confirm the important role of pairing interaction between the valence particles of a two-body halo system.

Island of inversion by microscopically derived shell-model Hamiltonian (Probing the nuclear force through direct reactions)

• Naofumi Tsunoda (University of Tokyo)

Room: Scotiabank Theatre We present the first application of the newly developed theory, EKK, of effective nucleon-nucleon interactions to the structure of exotic nuclei. This theory, a novel revision of many-body perturbation theory, enables us to perform shell-model calculations with several major shells (for instance, sd+pf shells). Using the Entem-Machleidt QCD-based chiral EFT interaction and the Fujita-Miyazawa three-body force, exotic neutron-rich Ne, Mg and Si isotopes are studied systematically, with a good description of ground-state energies, first 2+ and 4+ levels, and E2 transitions, as the first shell-model calculation for the island of inversion without two-body matrix elements fitted to experiment. The drip lines are predicted. We show effective single-particle energies from this interaction, exhibiting the shell evolution produced by the chiral EFT interaction + three-body force. Obviously, proposed configuration patterns can be exciting objects of direct reaction studies.

Description of transfer reactions with coupled-channels Born approximation (Theoretical developments of direct reactions)

• Tokuro Fukui (Nuclear Data Center, Japan Atomic Energy Agency)

Room: Scotiabank Theatre In order to theoretically describe transfer reactions, the distorted-wave Born ap- proximation (DWBA) is known to be a naive model and has brought about coincidence of calculated result with experimental data for some reactions. Recently, however, we have found that the DWBA is not able to be applied for some of the reactions, for instance, transfer reaction involving loosely bound nuclei, α-transfer reaction, and transfer reaction to continuum state of residual nucleus. In these cases the coupled-channels Born approximation (CCBA), in which the breakup effects of projectile and residual nucleus are taken into account by employing the method of the continuum-discretized coupled-channels (CDCC), could be one of powerful models to obtain reasonable result. First, we show that, for the CCBA analysis of the 8B(d,n)9C reaction, it is essentially important to consider the transfer process from (to) the breakup state of d (9C). These transfer process called the breakup transfer is never taken into account in the DWBA. Next, the importance of the CCBA model is given for the description of the α-transfer reaction 16O(6Li,d)20Ne, in which, so far the DWBA has been failed to produce the cross section to be consistent with measured one. Our calculation greatly improves coincidence of the calculation with the data and enables us to discuss the surface distribution of the α-cluster structure of 20Ne. Finally, how to describe transfer reaction to continuum state, such as α(d, p)5He, is presented. It is known that the integration in the transition matrix (T matrix) of such reaction does not converge. To avoid this problem, the prior form of the T matrix, for which the CCBA model is required to calculate the approximately exact wave function of the final channel, is employed.

Experimental study of $^{25-28}$O with SAMURAI (Invited)

• Yosuke Kondo (Tokyo Institute of Technology)

Room: Scotiabank Theatre The neutron drip line is one of the most fundamental nuclear properties and its shape on the nuclear chart reflects evolution of nuclear structure. It is experimentally known that $^{24}$O (N=16) is the most neutron-rich bound nucleus in oxygen isotopes while additional six neutrons can bound in $^{31}$F (N=22) for fluorine isotopes. The origin of the sudden change of the drip line, called oxygen anomaly [1], is unclear because many theories predict bound $^{26}$O and/or $^{28}$O, and cannot describe the location of the drip line for oxygen isotopes. Recent theoretical study [1] suggests that three nucleon forces play an important role in determining the neutron drip line of the oxygen isotopes. On the other hand, experimental data of the unbound oxygen isotopes beyond the drip line are not sufficient to examine theoretical studies quantitatively. Aiming at clarifying the mechanism of the oxygen anomaly, invariant mass spectroscopy of the unbound oxygen isotopes $^{25-28}$O has been performed. The experiment was carried out with the large acceptance spectrometer SAMURAI at RIBF. The unbound oxygen isotopes were produced by proton removal reactions from high intense RI beams provided by BigRIPS. Decay products were detected in coincidence by SAMURAI. Results of the study of the oxygen isotopes as well as recent activities at SAMURAI will be shown in the presentation. [1] T. Otsuka et al., Phys. Rev. Lett. 105, 032501 (2010). [2] T. Kobayashi et al., Nucl. Instrum. Methods Phys. Res., Sect. B317, 294 (2013).

Break up reactions with exotic nuclei and the impact of core excitations: from $^{19}$C to $^{31}$Ne (Theoretical developments of direct reactions)

• José A. Lay (Università di Padova - INFN Sezione di Padova)

Room: Scotiabank Theatre A successful and widely used tool for the understanding of halo nuclei has been the analysis of nuclear reactions within few-body reaction formalisms. In these analyses, one-neutron halo nuclei are treated as a valence-core two-body system assuming an inert core. This assumption is satisfied for the traditional one- and two-neutron halo nuclei like $^{11}$Be, although some evidences of core excitations can be found in its scattering. Present developments in radioactive beam facilities allows us to find new halo nuclei farther and farther from the stability line. These new cases will present more complex cores whose excitations will have an impact on the final cross sections. Recently, a great effort has been made in order to introduce the effect of a non-inert core in few-body reaction formalisms giving rise to the extensions of the DWBA (NR-XDWBA), the Faddeev/AGS equations and the CDCC (XCDCC). However, rather than a problem, it can turn into a great opportunity to deepen our knowledge of these new features. In this contribution we show how the inclusion of core excitations in the analysis of resonant break up opens the possibility of extracting spectroscopic information of the resonances of exotic nuclei [PRL109, 232502]. Experimental data for the break up of $^{19}$C and $^{23}$O on protons at intermediate energies [PLB660, 320 (2008); FBS54, 287 (2013)] will be analysed within XCDCC and NR-XDWBA. It will allow us to infer the structure of the resonances measured in $^{19}$C and $^{23}$O. Finally, the electromagnetic excitations of the core may compete with the dipole polarization of the halo nuclei. We will show how this affects to the study of halo nuclei through Coulomb dissociation and the extraction of the dipole electromagnetic transition probability B(E1) of $^{19}$C and $^{31}$Ne. We apply the recent extensions of the DWBA and CDCC including core excitations to analyze the resonant break up of $^{19}$C and $^{23}$O measured in [PLB660, 320 (2008); FBS54, 287 (2013)]. It allows us to infer structure information on the corresponding resonances of $^{19}$C and $^{23}$O. Strong evidences of core excitations in the present data are found. We also consider the effect of these core excitations in the Coulomb dissociation of halo nuclei. We conclude that it is compulsory to consider possible excitations of the core for the proper extraction of the B(E1) in halo nuclei like $^{19}$C and $^{31}$Ne.

Single-particle structure of ¹²Be studied in quasi-free (p,pn)-reactions (Shell evolution through direct reactions)

• Julian Kahlbow (Institut für Kernphysik, TU Darmstadt)

Room: Scotiabank Theatre The neutron-rich nucleus $^{12}$Be has been studied in inverse kinematics at the R$^3$B-LAND setup at GSI. In a kinematically complete measurement, proton-induced one-neutron knockout reactions at 400$~$MeV/nulceon are used to investigate single-particle properties. The high neutron-to-proton asymmetry leads to the breakdown of the magic $N=8$ shell-closure in $^{12}$Be. The valence-neutron pair configuration of the $^{12}$Be ground-state is assumed to be a mixture of the (1$p_{1/2}$)$^2$ occupation and the (2$s_{1/2}$)$^2$ & (1$d_{5/2}$)$^2$ intruder configuration above a $^{10}$Be core.[1,2] The bound and neutron-unbound states populated in the $^{11}$Be reaction fragment are disentangled by analysing the $\gamma$-ray spectrum and the relative-energy spectrum, respectively. All three partial cross sections are determined from quasi-free scattering and coherently analysed in eikonal reaction theory by C. A. Bertulani [3]. It is shown that the (2$s_{1/2}$)$^2$ & (1$d_{5/2}$)$^2$ intruder configuration is the dominant ground-state admixture in $^{12}$Be. This work is supported by HIC for FAIR, GSI-TU Darmstadt cooperation, and the BMBF project 05P15RDFN1. [1] A. Navin *et al.*, Phys. Rev. Lett. **85**, 266 (2000). [2] S. D. Pain *et al.*, Phys. Rev. Lett. **96**, 032502 (2006). [3] T. Aumann, C. A. Bertulani, and J. Ryckebusch, Phys. Rev. C **88**, 064610 (2013).

Probing neutron-proton correlation and 3N-force in $^{12}$C (Probing the nuclear force through direct reactions)

• Jenny Lee (The University of Hong Kong)

Room: Scotiabank Theatre Direct observation of neutron-proton (np) correlations and 3N-force in nuclei is the long-sought goal in nuclear physics. Two-nucleon knockout reactions offer a powerful tool as the reaction cross section is a direct probe of nucleon correlations. The experimental data of $^{12}$C on a carbon target reveal that the inclusive cross sections of residues from np removal channel ($^{10}$B) is approximately 6-8 times greater than those for nn pair (to $^{10}$C) and pp pair (to $^{10}$Be) [1,2], already in excess of the 16/6 ≈ 2.7 ratio from simple pair counting in $^{12}$C. Such enhancement however could not be described by the calculations using eikonal reaction dynamics and microscopic structure from the effective-interaction shell model and the no-core shell model with chiral NN+3N interactions [3]. To further investigate the nature of nucleon correlations and the origin of discrepancy between the observations and theories, we have performed the first final-state exclusive np-removal cross section measurements using DALI2 gamma-detection array and SAMURAI spectrometer at RIKEN. By the gamma-residue coincidence technique, the partial cross sections to $^{10}$B and $^{10}$Be T=0 and T=1 final sates following np and pp removal from $^{12}$C at 200 MeV/u were extracted. The experimental results indicate the insufficient treatment of T=0 np-correlations and 3N-force in the current microscopic structure models. In this talk, the experimental setup and the physics results will be discussed. [1] D. L. Olson et al., Phys. Rev. C. 28, 1602 (1983) [2] J. M. Kidd et al., Phys. Rev. C. 37, 6 (1988) [3] E. Simpson P. Navrátil, R. Roth, and J. A. Tostevin, Phys. Rev. C 86, 054609 (2012).

Study of neutron-neutron correlation in Borromean nucleus $^{11}$Li via the (p,pn) reaction (Exotic structures through direct reactions)

• Yuki Kubota (Center for Nuclear Study, The University of Tokyo)

Room: Scotiabank Theatre Dineutron correlation is one of the symbolic phenomena expected to appear in neutron drip-line nuclei. It has been studied using different approaches, such as the transfer reaction and the break up reaction. However, currently available data seem to be insufficient to study the neutron-neutron correlation in terms of (i) the decomposition of high-angular-momentum components, (ii) the extraction of a core excitation, (iii) and the effect of final state interactions (FSIs) [1]. In the present study, (i) the MINOS [2] was used for higher luminosity, (ii) $\gamma$ rays were detected to tag the core excitation, (iii) and the quasi-free $(p,pn)$ reaction was employed to minimize the FSI. In order to determine the momentum distribution of two valence neutrons, the kinematically complete measurement was performed. The opening angle between the two neutrons was reconstructed from the measured momentum vectors of all the particles. The experiment was carried out by using the SAMURAI spectrometer [3] combined with the liquid hydrogen target system MINOS. Momentum vectors of a knocked-out neutron and a recoil proton were respectively determined by the neutron detector WINDS [4] and a recoil proton detector setup, developed for this project. Decay neutrons and heavy fragments were momentum analyzed by the neutron detector NEBULA and the SAMURAI spectrometer, respectively. The details of experimental setup and results will be presented in this talk. [1] Y. Kikuchi et al., Phys. Rev. C 87, 034606 (2013). [2] A. Obertelli et al., Eur. Phys. Jour. A 50, 8 (2014). [3] T. Kobayashi et al., Nucl. Instr. Meth. B 317, 294(2013). [4] K. Yako et al., RIKEN Accel. Prog. Rep 45, 137 (2012).

First experimental signature of the giant pairing vibration in $^{14}$C and $^{15}$C nuclei (Invited)

• Diana Carbone (INFN - LNS)

Room: Scotiabank Theatre D.Carbone$^1$, F.Cappuzzello$^{1,2}$, M.Cavallaro$^1$, M.Bondì$^1$, C.Agodi$^1$, F.Azaiez$^3$, A.Bonaccorso$^4$, A.Cunsolo$^1$, L.Fortunato$^{5,6}$, A.Foti$^{2,7}$, S.Franchoo$^3$, E.Khan$^3$, R.Linares$^8$, J.Lubian$^8$, J.A.Scarpaci$^9$, A.Vitturi$^{6,7}$ $^1$INFN-Laboratori Nazionali del Sud, Catania, Italy $^2$Dipartimento di Fisica e Astronomia, Università di Catania, Catania, Italy $^3$Institut de Physique Nucleaire, Universitè Paris-Sud, Orsay, France $^4$INFN-Sezione di Pisa, Pisa, Italy $^5$Dipartimento di Fisica e Astronomia, Università di Padova, Padova, Italy $^6$INFN-Sezione di Padova, Padova, Italy $^7$INFN-Sezione di Catania, Catania, Italy $^8$Instituto de Fisica, Universidade Federal Fluminense, Niteroi, Brazil $^9$Centre de Sciences Nucleaires et de Sciences de Matieres, Universitè Paris-Sud, Orsay, France In 1977 Broglia and Bes predicted the existence of an elementary excitation mode, called Giant Pairing Vibration (GPV) [1]. Afterwards, many other theoretical papers were focused on the definition of the GPV, which is done in analogy with the Giant Resonances (GR) observed in almost all nuclei. The link between GPV and GR is the symmetry between particles and holes single particle states. Both of them are collective states, manifestation of a coherence mechanism of the particle-hole (GR) or particle-particle/hole-hole (GPV) excitations connecting major shell of the harmonic-oscillator-like mean field. The excitation of the GPV should be induced by two-nucleon transfer reactions with L = 0 angular momentum transfer. Despite the strong theoretical indications in favour of the existence of the GPV and many experimental attempts, a clear signature of it has been achieved only recently [2]. In this context, an experimental campaign was pursued at the Catania INFN-LNS laboratory by the ($^{18}$O,$^{16}$O) two-neutron transfer reaction at 84 MeV on different targets ($^{12}$C,$^{13}$C,$^{9}$Be,$^{11}$B,$^{16}$O). One of the qualifying aspects was the use of the MAGNEX spectrometer to detect the ejectiles. Indeed, thanks to its high resolution and large acceptance, high quality inclusive spectra were obtained, even in the region above the two-neutron emission threshold in the residual nucleus [3]. New phenomena appeared, such as the dominance of the direct one-step transfer of the two neutrons [4] and the presence of broad resonances at high excitation energy in the $^{14}$C and $^{15}$C spectra. The latter are associated with the first experimental indication of the GPV [2]. In the $^{14}$C nucleus it is identified at an excitation energy of 19.9 MeV with respect to the target ground state and in the $^{15}$C one at 20.4 MeV, values compatible with the GPV theoretical predictions by state-of-the-art cQRPA calculations on light nuclei [5]. The L = 0 nature of the transition to these resonances is suggested by model independent analysis of the measured cross section angular distributions by CRC calculations. Moreover, in a recent experiment, which explores the same $^{12,13}$C($^{18}$O,$^{16}$O)$^{14,15}$C reactions at 270 MeV incident energy, the observation of the GPV mode is confirmed with the same centroid and width. [1] R. A. Broglia and D. R. Bes, Phys. Lett. B 69, 129 (1977). [2] F. Cappuzzello et al., Nat. Commun. 6:6743 doi:10.1038/ncomms7743 (2015). [3] M. Cavallaro et al., J. Phys.: Conf. Ser. 381, 012094 (2012). [4] D. Carbone et al., J. Phys.: Conf. Ser. 312, 082016 (2011). [5] E. Khan et al., Phys. Rev. C 69, 014314 (2004).

The second 0$^+$ state of unbound 12O via the (p, t) reaction (Exotic structures through direct reactions)

• Daisuke Suzuki (Riken Nishina Center)

Room: Scotiabank Theatre We will present the recent finding of the second $0^+$ state in $^{12}$O, the lightest oxygen nucleus ever found, in our measurement of the $^{14}$O($p$, $t$) reaction at GANIL. $^{12}$O with $Z$ = 8 is a proton-rich mirror nucleus of $^{12}$Be with $N$ = 8. The level scheme of $^{12}$Be, including its intruder $0_2^+$ state at a very low excitation energy of 2.25 MeV, has been crucial in establishing the breakdown of the shell closure at $N$ = 8. The present search for the mirror $0_2^+$ state was thus aimed at investigating if the disappearance phenomenon of the shell closure also occurs at $Z$ = 8 and if so, how the $2s_{1/2}$ orbital intruding near the Fermi surface impacts the mirror symmetry between $^{12}$O and $^{12}$Be. Despite its importance, the spectroscopy of $^{12}$O has been challenging for decades as this nucleus is unbound for two-proton emission. In the present study, we measured the two-neutron transfer ($p$, $t$) reaction using a radioactive $^{14}$O beam at 51 MeV/u produced by the LISE spectrometer via the projectile fragmentation reaction. Missing-mass spectroscopy in inverse kinematics was realized by using MUST2 telescopes, each consisting of a double-sided silicon strip detector and a CsI calorimeter, to obtain resonance energies and differential cross sections of unbound states. The shell closure at $Z$ = 8 and the mirror symmetry with respect to $^{12}$Be will be discussed from the final result of the experiment.

Some aspects of the giant pairing vibration (Exotic structures through direct reactions)

• Augusto Macchiavelli (Lawrence Berkeley National Laboratory)

Room: Scotiabank Theatre The Giant Pairing Vibration (GPV), a correlated two-nucleon mode in the second shell above the Fermi surface, has long been predicted [1] and expected to be strongly populated in two-nucleon transfer cross sections similar to those of the normal Pairing Vibration (PV). Recent experiments have provided evidence for this mode in $^{14,15}$C [2] , but despite sensitive studies, it has not been definitively identified either in Sn or Pb nuclei where pairing correlations are known to play a crucial role [3]. In this work, we looked at whether features inherent to the mixing of bound and unbound levels might account for this intriguing puzzle. We study the effect of the mixing of unbound levels in a set of toy models that capture the essential physics of the GPV, along with a more realistic calculation including Distorted Waves Born Approximation (DWBA) transfer amplitudes. The calculated (relative) cross section to populate a simulated GPV state is effectively low, compared to the case of bound levels with no-widths, and the mixing turns out to be only a minor contributor to the weak population. Rather, the main reason is the melting of the GPV peak due to the width it acquires from the low orbital angular momentum single particle states playing a dominant role in two-nucleon transfer amplitudes. This effect, in addition to a severe Q-value mismatch [4], may account for the elusive nature of this mode in (t,p) and (p,t) reactions. [1] R. A. Broglia and D. R. Bes, Phys. Lett. B 69 129 (1977). [2] F. Cappuzzello, et al., Nat. Commun. 6:6743 doi: 10.1038/ncomms7743 (2015). [3] W. vonOertzen and A. Vitturi, Rep. Prog. Phys. 64 (2001) 1247; and references therein. [4] C. Dasso, H. Sofia, and A.Vitturi, Journal of Physics: Conf. Series 580 (2015) 012018.

Proton radii of neutron-rich isotopes from charge-changing cross section measurement (Invited)

• Alfredo Estrade (Central Michigan University)

Room: Scotiabank Theatre The measurement of the size of protons’ distribution in the atomic nuclei provides an experimental probe into exotic structure features that emerge in unstable isotopes, such as cluster and halo structures, and neutron skins. A Glauber model analysis of charge-changing cross section measurements can be used as a method to determine proton distributions of unstable isotopes, and offers the potential to reach nuclei very far from the line of $\beta$-stability. I will describe the work of our collaboration to perform charge-changing cross sections measurements at the fragment separator, FRS, at GSI. The talk will highlight recent experimental results for the radii of point proton distributions in neutron-rich beryllium and boron isotopes.

Charge-changing cross section measurement of neutron-rich carbon isotopes at 50A MeV and determination of their proton distribution root-mean-square radii by using Glauber model (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Dinh Trong TRAN (Research Center for Nuclear Physics, Osaka University, Japan)

Room: Scotiabank Theatre Root-mean-square (rms) radii and charge (proton) density distribution of proton in atomic nuclei are good observable for testing nuclear structure model. The proton distribution rms radius is important in extracting the neutron skin thickness, which provides guidance to constrain the theoretical description of the equation of state of asymmetric nuclear matter[1]. The electron scattering is a precise method to determine charge distribution rms radii[2], but could be applied only to stable nuclei. For unstable nuclei with Z < 5 and Z > 10, the isotope shift technique has been applied. However, it is difficult to extend to the drip line because of beam intensity limitation. This technique also become challenging for nuclei with 4 < Z < 11 due to the uncertainty in atomic physics calculation. The recent result on neutron-rich Be isotopes from charge changing cross section (CCCS) measurements at high energy were shown to be consistent with the isotope shift measurements[3], thus suggesting the possibility to determine proton density distribution as well as rms radii from CCCS using Glauber model. Recently, extended Glauber-type calculations were developed and applied to calculate the interaction/reaction cross sections. The calculated results show systematic agreement with experimental data over a wide range of energies[4, 5], suggesting possibility of applying the method to extract the rms of proton distribution radii from CCCS measurements at low energy region. We have measured the CCCSs of 12−18C isotopes at 50A MeV at RCNP, Osaka University. In this talk, the results of experiment is presented, and the feasibility of using our CCCS results to extract proton distribution rms radii via Glauber model will be discussed.

Study of proton distribution of neutron-rich nitrogen isotopes through charge-changing cross section measurements (Exotic structures through direct reactions)

• Soumya Bagchi (Saint Mary's University, Halifax, Canada and GSI, Darmstadt, Germany)

Room: Scotiabank Theatre S.Bagchi$^{1,2}$, R.Kanungo$^{1}$, F.Ameil$^{2}$, J.Atkinson$^{1}$, Y.Ayyad$^{3}$, D.Cortina-Gil$^{3}$, I.Dillmann$^{2}$, A.Estradé$^{1,2}$, A.Evdokimov$^{2}$, F.Farinon$^{2}$, H.Geissel$^{2,4}$, G.Guastalla$^{2}$, W.Horiuchi$^{5}$, R.Janik$^{6}$, M.Kimura$^{5}$, R.Knöbel$^{2}$, J.Kurcewicz$^{2}$, Yu.A.Litvinov$^{2}$, M.Marta$^{2}$, M.Mostazo$^{3}$, I.Mukha$^{2}$, C.Nociforo$^{2}$, H.J.Ong$^{7}$, S.Pietri$^{2}$, A.Prochazka$^{2}$, C.Scheidenberger$^{2,4}$, B.Sitar$^{6}$, P.Strmen$^{6}$, Y.Suzuki$^{8,9}$, M.Takechi$^{2}$, J.Tanaka$^{7}$, I.Tanihata$^{7,10}$, S.Terashima$^{10}$, J.Vargas$^{3}$, H.Weick$^{2}$, and J.S.Winfield$^{2}$ $^1$Saint Mary's University, Halifax, Canada $^2$GSI, Darmstadt, Germany $^3$Universidad de Santiago de Compostela, Santiago de Compostella, Spain $^4$Justus-Liebig University, Giessen, Germany $^5$Department of Physics, Hokkaido University, Sapporo, Japan $^6$Faculty of Mathematics and Physics, Comenius University, Bratislava, Slovakia $^7$RCNP, Osaka University, Mihogaoka, Ibaraki, Osaka, Japan $^8$Department of Physics, Niigata University, Niigata, Japan $^9$RIKEN Nishina Center, Wako, Saitama, Japan $^{10}$School of Physics and Nuclear Energy Engineering and IRCNPC, Beihang University, Beijing, People's Republic of China **Abstract** With large neutron-to-proton ratios far from the line of stability, nuclei develop exotic structures such as neutron skin and halo. Charge radius which is a fundamental nuclear ground-state property, seems to be changing with the increase of valence neutrons. As an example, the charge radius of $^{11}$Li, where there are two valence neutrons in addition to the core $^{9}$Li nucleus, is larger than that of $^9$Li [1]. Therefore, to understand the structure of neutron-rich nuclei, it is important to know how the proton distribution of a nucleus is affected with large neutron-to-proton ratios. A new tool to determine the point-proton root-mean-square radii in exotic nuclei is to measure the charge-changing cross section. Charge-changing cross section is the sum of all interactions of the protons in the projectile due to the collision with the nucleons of the target nucleus that changes the proton number of the projectile. Thus it can be used as a probe to measure the extent of the proton distribution in exotic nuclei through Glauber model analysis of the reaction. Measurements to determine the charge-changing cross section have been done for neutron-rich $^{8-11}$Li [2], $^{9-14}$Be [3], $^{15,16}$C [4], and $^{10-17}$B [5] isotopes. Here, we focus on similar systematic studies for neutron-rich nitrogen isotopes. Charge-changing cross sections of stable $^{14,15}$N isotopes and unstable $^{16-22}$N isotopes on a carbon target at relativistic beam energy of around 900 MeV/u have been measured precisely using the FRS fragment separator at GSI. In this presentation, the first preliminary observations for $^{14-16}$N will be discussed. **References** [1] R. Sánchez, *et al*., Phys. Rev. Lett. **96**, 033002 (2006). [2] B. Blank, *et al*., Z. Phys. A - Hadrons and Nuclei **343**, 375 (1992). [3] S. Terashima, *et al*., Prog. Theor. Exp. Phys. **101D02** (2014). [4] T. Yamaguchi, *et al*., Phys. Rev. Lett. **107**, 032502 (2011). [5] A. Estradé, *et al*., Phys. Rev. Lett. **113**, 132501 (2014).

Study of Gamow Teller strength from $^{132}$Sn via the inverse kinematics (p,n) reaction (Probing the nuclear force through direct reactions)

• Jumpei Yasuda (Department of Physics, Kyushu University)

Room: Scotiabank Theatre The Gamow-Teller (GT) transition is one of the basic excitation modes in nuclei. In medium or heavier mass region, the collectivity in this mode exhibits the GT giant resonance (GTGR), which gives information critically important for understanding the isovector part of effective nucleon-nucleon interaction[1]. Experimentally, charge-exchange (CE) reactions at intermediate energies have been used to extract the GT transition strength. Recently, the GT transitions from unstable nuclei can be studied by the development of a new experimental technique of CE (p,n) measurements in inverse kinematics[2]. We performed the measurement of the $^{132}$Sn(p,n) reaction at 220 MeV/u in inverse kinematics at RIBF in order to extract GT transitions strength from the key doubly-magic nuclei $^{132}$Sn. This is an essential step for establishing comprehensive theoretical models for nuclei situated in between $^{78}$Ni and $^{208}$Pb. The experiment was carried out by using the Wide-angle Inverse-kinematics Neutron Detectors for SHARAQ (WINDS)[3] and the large acceptance SAMURAI spectrometer[4]. A secondary beam of $^{132}$Sn was transported onto a 10-mm thick liquid hydrogen target, which was surrounded by WINDS to detect recoil neutrons. From the measured neutron time-of-flight and recoil angle, the excitation energy and center-of-mass scattering angle were determined. SAMURAI was used for tagging (p,n) reaction events with the particle identification of the outgoing heavy residues. Owing to the large momentum acceptance of SAMURAI, we can measure all the heavy fragments with different rigidities in one setting. It allows us to reconstruct the excitation energy spectrum up to high excitation energy including the GTGR. The details of experimental setup and experimental results will be presented in this talk. We also discuss the GT strength distribution on $^{132}$Sn. Reference [1] F. Osterfeld, Rev. Mod. Phys. 64, 491 (1992). [2] M. Sasano et al., Phys. Rev. Lett. 107, 202501 (2011). [3] K. Yako et al., RIKEN Accel. Prog. Rep 45 137 (2012). [4] T. Kobayashi et al., Nucl. Instr. Meth. B 317, 294 (2013).

A new probe into three-nucleon-force effects on reaction observables (Theoretical developments of direct reactions)

• Kosho Minomo (Research Center for Nuclear Physics, Osaka University)

Room: Scotiabank Theatre Understanding of the roles of three-nucleon forces (3NFs) in nuclear few- and many-body systems is one of the fundamental subjects in nuclear physics. Recently, 3NFs are constructed with chiral effective field theory in which two-, three-, and many-nucleon forces are treated consistently and systematically. The chiral 3NF effects have been analyzed in few-body systems and nuclear matter, and the binding energies of light nuclei and the saturation property in symmetric nuclear matter were well reproduced. Furthermore, it was found that the chiral 3NF effects improve the agreement between theoretical and experimental cross sections for nucleus-nucleus elastic scattering. We propose to use proton knockout reactions ($p$,2$p$) as a new probe into chiral 3NF effects on reaction observables. In many-body systems, 3NF effects can be represented by the density-dependence of nucleon-nucleon effective interaction. Proton knockout reactions from a deeply bound orbit must be suitable for probing 3NF effects since such reactions occur mainly in the internal region of the target nucleus in which the density is high. In this talk, we construct a microscopic framework of distorted-wave impulse approximation based on a nucleon-nucleon $g$-matrix interaction and microscopic optical potentials including chiral 3NF effects. And then, we analyze a kinematic condition which is favorable for probing the 3NF effects, and clarify the roles of chiral 3NF for knockout reactions. The chiral 3NF effects significantly change the peak height and full-width-at-half-maximum of the triple differential cross section of ($p$,2$p$) reactions.

Normal and intruder configurations in the island of inversion (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Kathrin Wimmer (The University of Tokyo)

Room: Scotiabank Theatre In the island of inversion a coexistence of low-lying states with different shapes results from the relatively small energy gap between normal, spherical $sd$ configurations and deformed intruder $fp$ configurations arising from excitations beyond the $N = 20$ shell gap. The ground states of these shape coexisting configurations have been identified in $^{30,32}$Mg, however, band-like structures built on top are yet to be identified. Additionally from the excitation energy of negative parity states, resulting from the coupling of $sd$ with $fp$ neutrons, the size of the shell gap can be determined. In-beam gamma-ray spectroscopy of $^{30,32}$Mg and surrounding nuclei has been performed in knockout reactions at the NSCL using the GRETINA gamma spectrometer coupled to the S800 spectrograph. Using different reaction channels, normal or intruder configurations can be populated selectively. We will present new results on the structure of $^{30,32}$Mg and discuss the transition into the island of inversion.

Knockout to probe proton contributions to the B(E2) transition strength in the C isotopes (Shell evolution through direct reactions)

• Heather Crawford (Lawrence Berkeley National Laboratory)

Room: Scotiabank Theatre The carbon isotopes represent one of the few cases where it is possible to obtain data from stability to the dripline, and to carry out no-core shell model ("ab-initio") calculations across the isotopic chain. Thus, data along the Z=6 isotopes can provide stringent constraints and tests of modern nuclear theories that aim to describe nuclear structure approaching the driplines. One experimental observable along the C chain that provides a sensitive probe of the details of the nucleon effective interactions is the B(E2) electric quadrupole transition strength. The B(E2) can provide information on the coupling between valence neutrons and the core, and any possible effects of weak-binding, particularly where the low-lying 2$^{+}$ state has a predominant neutron excitation. In the case of the C isotopes, changes in the observed B(E2) approaching the dripline are understood in terms of a changing proton contribution, rather than decoupling of the valence neutrons from the core at $^{20}$C, as was initially postulated. However, to draw final conclusions regarding the extent of any neutron decoupling, it is critical to know how the transition strength is partitioned between the protons and neutrons. Changes and uncertainties in proton occupation will dramatically influence the interpretation. I will report on the results of an experiment at NSCL to probe the amplitude of p-shell protons in the low-lying 2$^{+}_{1}$ states along the C isotopic chain through proton knockout from the corresponding N isotopes. By considering the cross-sections to populate the 2$^{+}$ excited states and 0$^{+}$ ground states in the C, we are able to constrain the proton contribution to the B(E2) transition strengths, and isolate any effects arising from neutron-core coupling.

Single-particle structure of $^{17}$C (Shell evolution through direct reactions)

• Jesus Pereira-Lopez (LPCCaen (France) / Universidade de Santiago de Compostela (Spain))

Room: Scotiabank Theatre Xesús Pereira-Lopez1,2, Beatriz Fernández-Domínguez1, Franck Delaunay2, Nigel A. Orr2, N. Lynda Achouri2, F. Miguel Marqués2, Julien Gibelin2, Wilton Catford3, Adrien Matta3, Diego Ramos1, Manuel Caamaño1, Valèrie Lapoux4, Anna Corsi4, Matthieu Sénoville4, Marlène Assie5, Benjamin Le Crom5, Nicolas de Séréville5, Fairouz Hammache5, Yorick Blummenfeld5, Iulian Stefan5, Daisuke Suzuki5, Maria Fisichella6, Geoff Grynier7, Mihai Stanoiu8, Florin Rotaru8, Marine Vandebrouck7, Thomas Roger7, Carme Rodriguez-Tajes7,1, Sylvain Leblond2, Andrew Knapton3, Alain Gillibert4, Emanuel Pollacco4, Pierre Morfouace5, Julien Pancin7, Emmanuel Clément7, Gilles de France7, Olivier Sorlin7, Jean-Charles Thomas7, Lucia Caceres7, Omar Kamalon7, Luc Perrot5, Beyhan Bastin7, Neil Curtis9, Carl Wheldon9, Tzany Wheldon9, Robin Smith9, Joe Walshe9, Sam Bailey9. 1 Universidade de Santiago de Compostela, 15754 Santiago de Compostela, Spain.<br> 2 LPC Caen, ENSICAEN, Université de Caen, CNRS/IN2P3, 14050 Caen, France.<br> 3 Department of Physics, Faculty of Electronics and Physical Sciences, University of Surrey, Guildford GU2 7XH, United Kingdom.<br> 4 IRFU, CEA-Saclay, 91191 Gif-sur-Yvette, France.<br> 5 Institut de Physique Nucléaire, Université Paris-Sud-11-CNRS/IN2P3, 91406 Orsay, France.<br> 6 Laboratori Nazionali del Sud, via S.Sofia 62, 95123 Catania, Italy.<br> 7 GANIL, BP 55027, 14706 Caen Cedex 5, France.<br> 8 IFIN-HH, P. O. Box MG-6, 76900 Bucharest-Magurele, Romania.<br> 9 School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, United Kingdom.<br><br> ---------- <br> The shell structure of stable and near-stable nuclei and the associated magic numbers are key elements in nuclear structure. It has been demonstrated, however, over recent years that the traditional magic numbers evolve when nuclei far from stability are explored. For example, recent experiments [1-3], including transfer studies by the TIARA collaboration at GANIL [4-6], have provided evidence to support the existence of a shell closure at N=16 in neutron-rich neon and oxygen isotopes associated with the vanishing of the N=20 shell gap. This has been understood as arising from the effects of the monopole part of the nucleon-nucleon interaction [7,8]. However, in the neutron-rich carbon isotopes, the extent to which the gap persist at N=16 is unclear. In an effort to answer this question we have attempted to probe the low-lying level structure of $^{17}$C using the $^{16}$C(d,p)$^{17}$C transfer reaction in inverse kinematics to locate the neutron single-particle orbitals involved in the formation of the N=16 shell gap. Of particular interest is the neutron 0d3/2 orbital, the spectroscopic strength of which is expected to be carried by unbound states. The experiment was carried out at the GANIL facility. A pure secondary beam of $^{16}$C at 17.2 AmeV produced by fragmentation in the LISE3 spectrometer was used to bombard a CD2 target. The light ejectiles were detected using with the TIARA and MUST2 silicon (Si) strip arrays while a Si-Si-CsI telescope was placed at zero degrees to identify beamlike residues. In addition, four HPGe-EXOGAM clover detectors were used to measure the gamma-rays arising from $^{17}$C bound excited states. The detailed goals of the experiment, the setup, the results of the analysis and a first interpretation will be discussed in this presentation. <br> [1] J. R. Terry et al., Phys. Lett. B, 640, 86 (2006).<br> [2] Z. Elekes et al., Phys. Rev. Lett., 98, 102502 (2007).<br> [3] C. R. Hoffman et al., Phys. Rev. Lett., 100, 152502 (2008).<br> [4] W. N. Catford et al., Phys. Rev. Lett. 104, 192501 (2010). [5] B. Fernandez-Dominguez et al, Phys. Rev. C 84, 011301 (2011).<br> [6] S. M. Brown et al., Phys. Rev. C 85, 011302 (2012).<br> [7] T. Otsuka et al., Phys. Rev. Lett. 105, 032501 (2010).<br> [8] T. Otsuka et al., Phys. Rev. Lett. 104, 012501 (2010).<br>

Inelastic proton scattering of Sn isotopes studied with GRETINA (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Christopher Campbell (Lawrence Berkeley National Laboratory)

Room: Scotiabank Theatre The chain of semi-magic Sn nuclei, with many stable isotopes, has been a fertile ground for experimental and theoretical studies. Encompassing a major neutron shell from N=50 to 82, the properties and structure of these nuclei provided important data for the development of the pairing-plus-quadrupole model. Recent experimental information on B(E2) for $^{106,108,110,112}$Sn came as a surprise as it indicated a larger collectivity than the predicted parabolic trend of quadrupole collectivity. These data, instead, show an unexpectedly flat trend even as the number of valence particles is reduced from 12 to 6. To fully understand how collectivity is evolving in these isotopes, $^{108,110,112}$Sn have been studied using thick-target, inelastic proton scattering with GRETINA tagging inelastic scattering events by detecting gamma-rays from the prompt decay of states excited in the reaction. We will present the trend of 2+ excitation cross-sections, the deduced quadrupole deformation parameters, and observations of other low-lying collective states. Comparison of these (p,p’) quadrupole deformation parameters with B(E2) data will provide new insights into the relative importance of proton and neutron contributions to collectivity in these nuclei. GRETINA was funded by the US DOE - Office of Science. Operation of the array at NSCL was supported by NSF under Cooperative Agreement PHY-1102511(NSCL) and DOE under grant DE-AC02-05CH11231(LBNL).

Isoscalar response of $^{68}$Ni to α-particle and deuteron probes (Invited)

• Marine Vandebrouck (GANIL)

Room: Scotiabank Theatre The study of the Isoscalar Giant Monopole Resonance (ISGMR) and the Isoscalar Giant Quadrupole Resonance (ISGQR) in stable nuclei provided relevant information on both nuclear matter and nuclear structure in past decades. For instance the ISGMR centroid can be linked to the incompressibility modulus of the infinite nuclear matter. Values for exotic nuclei would help in constraining it. In unstable nuclei, measurements in $^{56}$Ni have been performed [1-2]. In order to study the evolution of the ISGMR and the ISGQR along an isotopic chain, measurements in neutron-rich Ni are called for. To reach this goal, a dedicated experiment was performed at GANIL. A $^{68}$Ni beam at 50AMeV and with an intensity of 10000pps has been produced on LISE beamline. The inelastic scattering of deuteron and alpha particles on $^{68}$Ni in inverse kinematics has been studied with the active target MAYA [3-4]. It is the first attempt to measure the ISGMR in an unstable neutron-rich nucleus. Results concerning the inelastic scattering reaction in deuterons gas and in alpha gas will be shown, and the measurement of the ISGQR, ISGMR and indication of a soft mode will be discussed. REFERENCES [1] C. Monrozeau et al., Phys. Rev. Lett. 100, 042501 (2008). [2] S. Bagchi et al. Phys. Lett. B 751, 371 (2015) [3] M. Vandebrouck et al., Phys. Rev. Lett. 113, 032504 (2014). [4] M. Vandebrouck et al. Phys. Rev. C 92, 024316 (2015)

Isoscalar excitation of the PYGMY dipole resonance in $^{68}$Ni (Exotic structures through direct reactions)

• Nunzia Simona Martorana (INFN-Laboratori Nazionali del Sud, Via S. Sofia,62 Catania,Italy & Dipartimento di Fisica e Astronomia, Università di Catania, Via S. Sofia,64, Catania, Italy)

Room: Scotiabank Theatre ***N.S. Martorana***$^{a,b}$, L. Acosta $^{c,d}$, M.V. Andrés $^{e}$, G. Cardella $^{c}$, F.Catara $^{c}$, E. De Filippo $^{c}$, S.De Luca $^{f}$, D. Dell'Aquila $^{g}$, B.Gnoffo $^{c}$, E.G. Lanza $^{c}$, G. Lanzalone $^{a,h}$, I. Lombardo $^{g}$, C.Maiolino $^{a}$, S. Norella $^{f}$, A. Pagano $^{c}$, E.V. Pagano $^{a,b}$, M. Papa $^{c}$, S. Pirrone $^{c}$, G.Politi $^{b,c}$, L. Quattrocchi $^{f}$, F. Rizzo $^{a,b}$, P. Russotto $^{c}$, A. Trifirò $^{f}$, M. Trimarchi $^{f}$, M. Vigilante $^{g}$, A. Vitturi $^{i}$. $^{a}$ INFN-Laboratori Nazionali del Sud, Via S. Sofia,62 Catania,Italy $^{b}$ Dipartimento di Fisica e Astronomia, Università di Catania, Via S. Sofia,64, Catania, Italy $^{c}$ INFN-Sezione di Catania, Via S. Sofia 64, Catania, Italy $^{d}$ Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Mexico City,Mexico $^{e}$ Departamento de FAMN,Universidad de Sevilla, Sevilla, Spain $^{f}$ INFN Gruppo collegato di Messina & Dipartimento di Fisica,Università di Messina,Messina,Italy $^{g}$ INFN-Sezione di Napoli & Dipartimento di Fisica, Università Federico II, Napoli, Italy $^{h}$ Facoltà di Ingegneria e Architettura, Università Kore, Enna, Italy $^{i}$ INFN-Sezione di Padova & Dipartimento di Fisica,Università G. Galilei, Padova, Italy In the last years much attention has been devoted to the study of collective states in neutron-rich nuclei. In particular, the presence of electric dipole response around the nucleon binding energy, that is far from the well known Giant Dipole Resonance, is of remarkable interest [1,2]. This mode, the so-called Pygmy Dipole Resonance (PDR), although is carrying few per cent of the isovector Energy Weighted Sum Rule (EWSR) has a strong relation with the symmetry energy and it has been used as a further tool to constrain it. It is predicted to be present in almost all nuclei with neutron excess: in particular for nuclei far from the stability line. This new mode can be populated by both isoscalar and isovector probes due to the properties of its transition densities [3]. Most of these experiments, with both probes, have been performed on stable nuclei [1,2], with only two exception where the relativistic Coulomb excitation was used. We report here, for the first time, preliminary results on an experiment done in inverse kinematics using an unstable projectile on an isoscalar target. We performed at LNS-INFN of Catania, an experiment using a $^{68}$Ni beam at 40 MeV/nucleon impinging on a $^{12}$C target, produced by In Flight Fragmentation method in a dedicated In Fligth Radioactive Ion Beams (FRIBs) transport line. The detector systems CHIMERA [4] and Farcos [5] were used to detect both gamma and charged products. [1] D. Savran, T. Aumann and A. Zilges, Prog. Part. Nucl. 
Phys. 70, 210 (2013). [2] A. Bracco, F.C. L. Crespi, and E. G. Lanza, Eur. Phys. J. A 51 (2015).
 [3] E. G. Lanza, A. Vitturi, M. V. Andrés, F. Catara and D. Gambacurta, Phys. Rev. C 84, 064602 (2011). [4] A.Pagano et al Nucl.Phys. A 734 (2004) 504. [5] L. Acosta et al., EPJ Web of Conferences, 31 ,0035 (2012).

Investigation of $^{11}$Li excited state through proton inelastic scattering (Exotic structures through direct reactions)

• Junki Tanaka (RCNP)

Room: Scotiabank Theatre The ground state of $^{11}$Li is known as a two neutron halo nucleus and some unconventional phenomena originated from the halo. These include the large matter radius, small two neutron separation energy, narrow component of two neutrons' momentum distribution. The excited resonant states of $^{11}$Li are also expected to have some halo influenced features but because of the experimental challenges, those are not yet well understood. Especially because of its weakly bound two neutrons, we expected the appearance of multipole excitations in low excitation energy. We aimed to investigate the excited resonant states of $^{11}$Li through proton inelastic scattering. This was done using the facility with a solid H$_2$ target, IRIS(ISAC Charged Particle Reaction Spectroscopy Station) at TRIUMF. The window-less solid hydrogen target provides us the scope of attaining good statistics while achieving also a high excitation energy resolution ~ 400 keV in FWHM. The excitation energy spectrum of $^{11}$Li was constructed by missing mass method. The results of this new experiment will be presented which show a prominent peak at around 0.80 MeV. This peak is at a lower energy than the soft dipole resonance peaks reported in earlier studies. DWBA calculations with a collective vibrational model excitation form factor were performed in order to understand the type of excitation. A comparison of these calculations with the angular distribution of the peak indicates an $l$=0 transition. This suggests the possibility of a new soft monopole excitation.

Neutron transfer reactions with exotic tin beams and neutron capture (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Jolie Cizewski (Rutgers University)

Room: Scotiabank Theatre Neutron capture at late times in r process nucleosynthesis can have significant impact on the observed r-process abundances. In particular, uncertainties in neutron capture rates near $^{130}$Sn significantly impact network calculations of r-process abundances not only near $^{132}$Sn but also for heavier nuclei [1]. We have recently completed the analysis of the (d,p) reactions with exotic A=132,130,128,126 and stable A=124 tin beams accelerated to ≈5 MeV/u at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. Measurements were made with CD2 targets. In the $^{124,126,128}$Sn measurements, light reaction products were measured with the Super Oak Ridge Rutgers University Barrel Array (SuperORRUBA) of highly segmented silicon strip detectors supplemented by the Silicon Detector Array (SIDAR) at back angles in the laboratory. Previous measurements of the $^{130,132}$Sn reactions [2,3] were combined with the $^{124,126,128}$Sn results to extract spectroscopic factors using the same Finite Range Adiabatic Wave Approximation (FR-ADWA) formalism [4]. Direct-semi-direct (DSD) neutron capture was calculated with the CUPIDO code [5] constrained by empirical spectroscopic factors for 2f7/2, 3p3/2, and 3p1/2 states in odd A=125-133 Sn isotopes. The deduced DSD cross sections are significantly smaller than previous estimates [6]. Below $^{132}$Sn, the role of statistical neutron capture, modeled in the Hauser-Feshbach framework, is expected to become increasingly important. To determine this component of the (n,$\gamma$) cross section requires a surrogate, for example the (d,p$\gamma$), reaction with exotic beams. The current collaboration has commissioned the Gammasphere-ORRUBA Dual Detectors for Experimental Structure Studies (GODDESS) with the capability to measure inverse kinematics (d,p$\gamma$) reactions and validating this reaction as a surrogate for (n,$\gamma$). The present contribution would present the DSD results from the Sn(d,p) campaign and the status of the efforts to develop a valid surrogate for statistical neutron capture on short-lived nuclei. This research by the ORRUBA Collaboration is supported in part by the U.S. Department of Energy and National Science Foundation. [1] M.R. Mumpower, R. Surman, G.D. McLaughlin, A. Aprahamian, arXiv:1508.07352v1 and JPPNP (in press); and references therein. [2] K.L. Jones et al., Nature **465**, 454 (2010), K.L. Jones et al., Phys. Rev. C **84**, 034601 (2011). [3] R.L. Kozub et al., Phys. Rev. Lett. **109**, 172501 (2012). [4] I.J. Thompson, Comp. Phys. Rep. **7**, 167 (1988). [5] G. Arbanas, F.S. Dietrich, A.K. Kerman, *Perspectives on Nuclear Data for the Next Decade*, p. 105 (2005). [6] S. Chiba et al., Phys. Rev. C **77**, 015809 (2008).

Transfer reactions on high-spin nuclear isomers (Probing the nuclear force through direct reactions)

• Daniel Santiago-Gonzalez (Louisiana State University)

Room: Scotiabank Theatre The use of isomer beams has potential to probe aspects of nuclear structure which are otherwise inaccessible from reactions with beams of nuclei in their ground state. For example, studies of the single-particle component of high-spin states, as well as studies on how core excitations affect nuclear structure can be carried out via transfer reactions in inverse kinematics on high-spin isomer beams. In order to demonstrate the feasibility of this technique, we have performed an experiment to populate high-spin states in $^{19}$F via the ($d$,$p$) neutron-transfer reaction on an isomer beam of $^{18}$F. The $^{18}$F beam was produced at the Argonne Tandem Linac Accelerator System using the in-flight technique. The resulting $^{18}$F beam consists of a mixture of the $5^+$ isomer and the $1^+$ ground state. The $^{18}$F beam was transported to the HELIOS spectrometer, which was used to analyze outgoing protons following the ($d$,$p$) reaction on the ground state and 5$^+$ isomer of $^{18}$F. The reconstructed excitation energy spectrum of $^{19}$F indicates direct population of the $13/2^+$ state which, in this case, can only be reached from reactions with the isomer component of the beam. Preliminary results suggest the $13/2^+$ is the terminating state of the ground-state rotational band of $^{19}$F.​ This material is based upon work supported by the U.S. Department of Energy, Office of Nuclear Physics, under contract No. DE-AC02-06CH11357 and No. DE-FG02-96ER40978. This research used resources of ANL's ATLAS facility, which is a DOE Office of Science User Facility.

Probing nuclear sizes of unstable nuclei with total reaction cross sections (Invited)

• Wataru Horiuchi (Hokkaido University)

Room: Scotiabank Theatre Measuring nuclear sizes has a long history. The nuclear charge distribution (radius) is traditionally determined by electron scattering measurement. However, thus far probing neutron distribution is difficult, and the measurement is limited to stable nuclei. Total reaction or interaction cross section is known as a quantity that reflects nuclear sizes. Using recent rare isotope beam facilities, the cross section can be measured for almost all nuclei as long as they are produced in sufficient number. In this talk, we present our recent studies on nuclear size properties of unstable nuclei using total reaction cross sections, especially focusing on nuclear deformation and neutron-skin thickness. Incident energy and target dependence of the cross section is discussed in order to select appropriate reactions for the size determination. If time allows, feasibility of determining the proton radius of unstable nuclei using charge-changing cross section, which can be measured in the same setup of the total reaction cross section.

Search for new halo states in nuclear ground and excited states with fast rare isotope beams (Exotic structures through direct reactions)

• Nobuyuki Kobayashi (National Superconducting Cyclotron Laboratory)

Room: Scotiabank Theatre The possible appearance of nuclear halos in the ground and excited states close to the particle-decay threshold is of great importance for investigating nuclear structure and few-body correlations at the limit of stability. In this presentation, first I will discuss recent experimental results regarding a moderate halo formation in the ground state of $^{29}$Ne. Next, I will introduce a novel method to measure the interaction cross sections of excited states. The former topic aims at finding halo formation in the vicinity of the island of inversion, which is important to study $fp$-shell intruder configurations at $N$ = 20 magic number. This is accomplished through a combined investigation of nuclear and Coulomb-induced one-neutron removal reactions at 240 MeV/nucleon. The results indicate that the ground state of $^{29}$Ne has spin parity of 3/2$^-$ and is dominated by a large $p$-wave component. The discussion will be detailed in the presentation. The latter topic is intended to identify a new halo formation in excited states. The method utilizes a combination of the transmission method and recoil distance method with a plunder device, enabling us to measure the number of reactions of the excited states in a target. I will discuss basic ideas of this method and required experimental setups. This consideration provides a totally-new opportunity to perform reaction studies on the excited states of rare isotopes.

Linking nuclear reactions and nuclear structure to predict neutron skins (Theoretical developments of direct reactions)

• W. H. Dickhoff (Washington University in St. Louis)

Room: Scotiabank Theatre The dispersive optical model (DOM), originally conceived by Claude Mahaux$^{1}$, provides a unified description of both elastic nucleon scattering and structure information related to single-particle properties below the Fermi energy. Recent extensions of this framework have introduced a fully nonlocal implementation for ${}^{40}$Ca$^{2}$. For the first time properties below the Fermi energy like the charge density and the presence of high-momentum nucleons can be included in the DOM description while elastic cross section data can be represented as accurately as in the local DOM implementation. The nonlocal DOM is furthermore capable of determining the spectral strength distribution at positive energy of orbits which are bound$^{3}$. These distributions depend sensitively on the location of the energy of the orbit in question exhibiting a strong increase for those orbits that are very weakly bound and therefore behave like valence orbits in exotic nuclei. These spectral distributions are constrained by elastic scattering data which can therefore provide direct information about correlation effects in exotic nuclei. Recent extensions of the nonlocal DOM to ${}^{48}$Ca incorporate the effect of the 8 additional neutrons and allow for an excellent description of elastic scattering data of both protons and neutrons${}^4$. The measured charge density of this nucleus is also accurately described. The corresponding neutron distribution constrained by all available data generates a prediction for the neutron skin of 0.249 $\pm$ 0.023 fm for this nucleus${}^{4}$ which is larger than most mean-field and available ab initio results. Extensions to a nonlocal DOM implementation for ${}^{208}$Pb are in progress. [1] C.Mahaux and R.Sartor, $Adv.Nucl. Phys.$ 20, 1 (1991). [2] M.H.Mahzoon $et\ al.$, $Phys. Rev. Lett.$ 112, 162503 (2014). [3] H.Dussan $et\ al.$, $Phys. Rev. C$ 90, 061603(R) (2014). [4] M.H.Mahzoon, Ph.D. thesis, Washington University in St. Louis (2015).

1pxn removal cross sections of light exotic nuclei and the role of final state interactions in projectile fragmentation (Exotic structures through direct reactions)

• Ronja Thies (Chalmers University of Technology)

Room: Scotiabank Theatre Reaction cross sections of exotic nuclei have given rise to several interesting discoveries like halo-structure. Reaction cross sections are model-independent observables which can be obtained from inclusive measurements. We have systematically measured 1pxn removal cross sections for (10,12-18)C and (10-15)B isotopes impinging at relativistic energies onto a carbon target using one experimental set-up, thus reducing (systematic) uncertainty. A number of very successful models exist for describing reaction cross sections, but those are benchmarked against stable beam experiments. We test the abrasion-ablation model ABRABLA07 [1] and EPAX [2] with our consistent dataset of cross sections from exotic nuclei. We also study the dependence of ABRABLA07 on the average excitation energy induced per abraded nucleon using our data and complementary results from literature. We see an interesting and unexpectedly regular behaviour of the fragmentation cross sections – usually preferring the production of a stable or semi-magic daughter nucleus. We find that the average excitation energy per abraded nucleon has to be decreased for our light nuclei. Additionally we find a mass dependence of the best fit excitation energy. Nevertheless the data also shows that the mass is not the only parameter influencing the average induced excitation energy per abraded nucleon. By lowering the average excitation energy, the experimental data are reproduced surprisingly well, especially since the model is intended for medium-mass to heavy nuclei. [1] J.-J. Gaimard and K.-H. Schmidt , Nucl. Phys. A531, 709 (1991). [2] K. Sümmerer and H. Weick (C translation), [C source code] EPAX Version 3 (2013).

MUGAST: an highly-segmented particle array for the forthcoming science campaign with radioactive beams at GANIL (New instrumentation for direct reaction studies of exotic nuclei)

• Daniele Mengoni (University and INFN - Padova)

Room: Scotiabank Theatre MUGAST is a state-of-the-art silicon array, including MUST[1], GASPARD[2] and TRACE[3] detectors, that allows reaction and structure studies in combination with gamma-ray tracking spectrometers and enables the possibility to use, in the near future, the innovative PSA technique, developed by our collaboration[4]. The MUGAST configuration provides a large angular coverage that allows the study of stripping reaction such as (d,p),(3He,d), (3He,p), (6Li,d), etc., which requires detection of the recoil particle at angles ranging from the very backward angles to 90 degrees or lower, while being compatible with the present AGATA[5] configuration, as it is installed at VAMOS[6]. In fact, the high-granularity of the silicon array has been natively designed for optimal integration in new-generation gamma-ray tracking detectors with the aim of performing high-resolution studies. This will allow a very large gain in excitation energy resolution, in comparison with the case where the excitation energy is deduced from the recoil charged-particle measurement. The MUGAST array has been designed to be compatible with the cooled-gas 3He or 4He target, as the one developed at IPNO for MUST2 experiments, as well as the conventional solid targets, such as CH2, CD2, LiF. The significant development in the instrumentation led to the compelling proposition of combining MUGAST+AGATA with the magnetic spectrometer VAMOS, with the aim to deliver a campaign around transfer reactions as a core component of the future scientific programme at GANIL, in 2018. Much interest has been demonstrated by the the large number of LoIs submitted for the future campaign, ranging from shell evolution to nuclear astrophysics. The present contribution focuses on the status and progresses of the project and the future physics campaign outlined at GANIL by using the upgraded SPIRAL1 facility. [1] Y.Blumenfeld et al., Nucl. Inst. and Meth. A421, (1999) 471. [2] D.Beaumel, Nucl. Inst. and Meth. B317, (2013) 661. [3] D.Mengoni et al., Nucl. Inst. and Meth. A764, (2014) 241. [4] M.Assie et al., Eur. Phys. Jour. A51, (2015) 11. [5] S.Akkoyun et al., Nucl. Inst. and Meth. A668, (2012) 26. [6] M. Rejmund et al., Nucl. Inst. and Meth. A646, (2011) 184.

Coupling gamma-ray detection to an active target in a high magnetic field: the SpecMAT project for direct reaction studies (New instrumentation for direct reaction studies of exotic nuclei)

• Tommaso Marchi (KU Leuven Department of Physics and Astronomy Instituut voor Kern- en Stralingsfysica)

Room: Scotiabank Theatre SpecMAT (Spectroscopy of exotic nuclei in a Magnetic Active Target) entails the development of a new active target detector, surrounded by an array of scintillators and placed in a high magnetic field. The setup will operate at HIE-ISOLDE (CERN), where a 4 Tesla solenoid will be installed in a dedicated beam-line. The HIE-ISOLDE facility is already providing post-accelerated radioactive ion beams with energies up to 4 AMeV, which will rise to 10 AMeV in forthcoming years. This unique combination of beams and instrumentation will allow studying nucleon transfer reactions in inverse kinematics, even with very low intensity beams, thereby widening the scope of research to the most exotic nuclei. The main goal of the project is to perform complete nuclear spectroscopy studies in the neutron-rich nuclei around Z = 28 and in the neutron-deficient nuclei around Z = 82, tackling open issues such as the evolution of nuclear shells and magic numbers, as well as answering questions about shape coexistence in those regions. In addition to the well-known advantages of the active target approach, such as high luminosity and high efficiency, the combined use of scintillators will allow for the detection of coincident gamma-rays, providing complementary spectroscopic information. At the same time, light charged particle trajectories will be reconstructed by measuring their spiral motion inside the magnetic field. This configuration should allow for the measurement of binary reactions with an improved dynamic range with respect to conventional active targets. The main goals of the SpecMAT project and the present status will be illustrated. The contribution will then focus on the development of the scintillation array and on the status of the GEANT4 simulation of the device and tracking algorithms. The project is funded by the EU under ERC consolidator grant n.617156.

Multi-nucleon transfer reactions populating neutron-rich actinide nuclei for fission study (New instrumentation for direct reaction studies of exotic nuclei)

• Katsuhisa Nishio (Advanced Science Research Center, Japan Atomic Energy Agency)

Room: Scotiabank Theatre We are promoting a campaign to study multi-nucleon transfer reactions to populate excited states in neutron-rich actinide nuclei which cannot be accessed by particle capture and/or fusion reactions. Main purpose of this program is to study fission in new region of chart of nuclei. As a first step we studied reactions using the $^{18}$O beam ($\sim$ 9MeV/u) and actinide target nuclei such as $^{238}$U, $^{237}$Np, $^{248}$Cm. The experiment was carried out at the tandem facility of Japan Atomic Energy Agency. Ejectile nuclei generated in the reaction were identified by a newly developed silicon $\Delta$E-E detectors ($\Delta$E=75$\mu$m, $E=$300$\mu$m). Using this detector, clear separation up to oxygen isotopes ($^{16,17,18,19}$O) was obtained as well as lighter element isotopes (Be, B, C, N). The number of produced nuclei amounted to more than fifteen in one reaction. Two fragments emitted in multi-nucleon transfer fission were detected by multi-wire proportional counters, and fission fragment mass distributions (FFMDs) were measured for each isotopes. In the comparison of measured FFMDs with a calculation based on the fluctuation-dissipation model, it was found that the excited states up to more than 60MeV was populated. Measurement of fission fragment angular distribution relative to the recoil direction suggested the increase of the spin with the number of transferred nucleons.

Direct rections for studies of nuclei beyond the drip-lines in correlation experiments at ACCULINNA-facility (New instrumentation for direct reaction studies of exotic nuclei)

• Yulia Parfenova (LNR, JINR, Dubna)

Room: Scotiabank Theatre To answer a foundamental question concerning the nuclear stability it is necessary to break through to extremely neutron- and proton- reach nuclei at the drip-line and beyond it, where nuclei exist as short-living resonances. For studies of such nuclei radioactive beams are used. During the last 15 years in the Flerov Laboratory of Nuclear reactions ( JINR, Dubna, Russia) the ACCULINNA-facility was used for the experimental studies at intermediate energies 20-60 A MeV. At these energies the direct reactions are the most effective tool for studies of nuclear structure in exchange, transfer reactions, and quasi-free scattering. An important advantage of these energies is relatively intensive population of strongly alligned states allowing spin and parity identification. Instead of measurements of angular distributions in the inelastic scattering of unstable nuclei, the much less known method, based on measurements of angular correlations in decays of the unstable nuclei formed in the reactions, is used. The correlation data showed to be a powerful tool for studies of the exotic nuclear structure and decay dynamics. But their measurements complicate the experimental setup and theoretical analysis. The experimental data are biased by experimental setup making impossible direct comparison of the experimental data with theory. This problem can be handled by application of the MC simulations of the experimental "events" generated within theoretical models. All these aspects of the exotic nucleai studies at the ACCULINNA-facility, i.e. experimental studies, MC simulations, theoretical model analysis, and theoretical model development are handled at LNR JINR. In this vein, experimental and theoretical studies of 3-body unstable nuclei 6Be, 6,8,10He, 5,7H, 17Ne are performed.

Neutron orbits near doubly-magic $^{78}$Ni and $^{132}$Sn from reactions with radioactive beams (Invited)

• Riccardo Orlandi (Japan Atomic Energy Agency, Advanced Science Research Center)

Room: Scotiabank Theatre Transfer reactions are a valuable tool to study the evolution of shell structure away from stability. In particular, studies of nuclei in the proximity of exotic doubly-magic nuclei like $^{78}$Ni and $^{132}$Sn are key systems to test our theoretical understanding, since the proximity of the doubly-magic core makes shell-model calculations feasible. Single-neutron states in the Z=30, N=49 isotope $^{79}$Zn have been populated using the $^{78}$Zn(d,p)$^{79}$Zn transfer reaction in inverse kinematics at REX-ISOLDE, CERN. The experimental setup allowed the combined detection of protons ejected in the reaction, and of γrays emitted by $^{79}$Zn. From the combined analysis of γ-ray and proton data, low-lying states in $^{79}$Zn were observed and identified. Comparison with large-scale shell-model calculations permits to constrain the size of the N=50 shell gap in $^{78}$Ni. Neutron-hole states in $^{131}$Sn were populated using the $^{132}$Sn(d,t)$^{131}$Sn reaction at the HFRIB facility at Oak Ridge National Laboratory. Measured proton differential cross sections and their impact of single-hole energies in $^{132}$Sn will also be presented.

Single particle structure and shapes of exotic Sr isotopes (Shell evolution through direct reactions)

• Steffen Cruz (UBC, TRIUMF)

Room: Scotiabank Theatre Nuclei near the so called magic numbers of protons and neutrons are observed to have a spherical shape in their low lying states. Nuclei between magic numbers, where the binding energy tends to be less, are often observed to show deformation in low lying states. These deformations have either a prolate or oblate nature. States within a nucleus that have different shapes that are close in energy are colloquially referred to as shape coexisting. A dramatic occurrence of shape coexisting states is observed in nuclei in the vicinity of Z=40, N=60, which is the subject of substantial current experimental and theoretical effort. An important aspect in this context is the evolution of single particle structure for N<60 leading up to the shape transition region, which can be calculated with modern large scale shell model calculations using a $^{78}$Ni core or Beyond Mean Field Models. One-neutron transfer reactions are a proven tool to study single-particle energies as well as occupation numbers. Here we report on the study of the single-particle structure in $^{95,96,97}$Sr via (d,p) one-neutron transfer reactions in inverse kinematics. The experiments presented were performed in the ISAC facility using the TIGRESS gamma-ray spectrometer in conjunction with the SHARC charged-particle detector. Highly charged beams of $^{94,95,96}$Sr, produced in the ISAC UCx target and charge-bred by an ECR source were accelerated to 5.5 MeV/A in the superconducting ISAC-II linac before delivery to the experimental station. Other than their clear scientific value, these measurements were the first high mass (A>30) post-accelerated radioactive beam experiments performed at TRIUMF. A thorough analysis of single particle states will improve our understanding of the onset of these unique structures, encouraging the ongoing theoretical discussions. Through $^{95}$Sr(d,p) a strong occupation of the first excited 0$^{+}$ state and a weak population of the second 0$^{+}$ state was measured. This suggests that there is strong mixing between the ground state and the first 0$^+$. These results discussed in the context of the evolution of single-particle structure will be presented.

Shell evolution toward the island of inversion with $^{29}$Mg (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Adrien Matta (University Of Surrey)

Room: Scotiabank Theatre The "Island of Inversion" refers to a group of very neutron rich nuclei centred on $^{30}$Ne and $^{32}$Mg, in which the gap in energy at N=20 between the $1s0d$ and $0f1p$ shells has become sufficiently small to allow the latter configurations to dominate the ground states, effectively favouring particle-hole configurations. One of the keys to understanding the "Island of Inversion" lies in the evolution of the orbital energies as we move from stable nuclei into this region. The $^{28}$Mg($d$,$p$)$^{29}$Mg reaction offers detailed probing of the neutron orbitals and interactions that determine the properties of the more neutron-rich isotopes where the "Island of Inversion" becomes fully developed. The details that are hidden in the properties of $^{32,34}$Mg are exposed and quantified in the structure of $^{29}$Mg. The changes in the relative energies of shell model orbits, depending on the neutron/proton balance in the nucleus, cause level energies to evolve and therefore change the shell gaps and their corresponding magic numbers, effectively replacing N=20 by N=16. This can be studied most effectively by means of single nucleon transfer reactions. The ($d$,$p$) reaction is an ideal tool to probe this behaviour, as it allows the transfer of a neutron into the $0d3/2$, $0f7/2$, $1p3/2$ and higher lying orbitals, and the energies of the observed states relate directly to the spacing between the $sd$ and $fp$ orbitals at $N$=20. We will present results obtained recently at TRIUMF in inverse kinematic, using a $^{28}$Mg beam produced and reaccelerated by the ISAC-II facility. The $^{29}$Mg spectroscopy was studied via the missing mass method and particle-gamma coincidences obtained from the combination of SHARC and TIGRESS arrays. Recently obtained results on $^{29}$Mg spectroscopy studied via ($d$,$p$) using the SHARC and TIGRESS arrays will be presented. The $^{28}$Mg($d$,$p$)$^{29}$Mg reaction offers detailed probing of the neutron orbitals and interactions that determine the properties of the more neutron-rich isotopes where the "Island of Inversion" becomes fully developed. The details that are hidden in the properties of $^{32,34}$Mg are exposed and quantified in the structure of $^{29}$Mg.

Recent results on direct reactions with stored radioactive beams and with active targets (New instrumentation for direct reaction studies of exotic nuclei)

• Peter Egelhof (GSI Helmholtzzentrum für Schwerionenforschung)

Room: Scotiabank Theatre The investigation of direct reactions with radioactive beams in inverse kinematics has already been proven to be a valuable tool for providing important information on the structure of exotic nuclei. In particular, it turned out that in many cases essential nuclear structure information can be deduced from high-resolution measurements at low momentum transfer. Such experiments can favourably be performed either by using the experimental technique of active targets, or, with even higher luminosities, with the new and innovative method of using stored and cooled radioactive beams interacting with thin internal targets at storage rings. The latter technique, due to the thin windowless targets and to beam cooling, enables high resolution measurements down to the region of low momentum transfer with very low recoil energies, and provides a gain in luminosity from accumulation and recirculation of the radioactive beams. Consequently a dedicated innovative experimental setup was designed, constructed, and installed at the ESR storage ring at GSI by the EXL [1] collaboration, and successfully used for a – even on a world-wide scale – first reaction experiment with a stored radioactive beam. The experimental concept will be discussed and the results of the experiment with a stored radioactive 56Ni beam, where the nuclear matter distribution of the doubly magic 56Ni nucleus was investigated by elastic proton scattering, and a feasibility study on 58Ni(α,α`) inelastic scattering, where it was demonstrated that the Giant Monopole Resonance in 58Ni can be investigated by the present technique down to cm angles below 1 degree, will be presented. As alternative method for low momentum transfer measurements, in particular for very short lived nuclei with lifetimes below 1 sec, the technique of active targets is well suited. An overview on recent results, obtained with the IKAR active target on nuclear matter distributions of the proton halo candidate 8B, and of neutron rich carbon isotopes, obtained from intermediate energy elastic proton scattering, will be presented. [1] EXL: EXotic nuclei studied in Light-ion induced reactions at the NESR storage ring

Elastic scattering of weakly bound nuclei $^{8}$B and $^{9,10,11}$C on $^{nat}$Pb target (Exotic structures through direct reactions)

• Yanyun Yang (Institute of Modern Physics, Chinese Academy of Sciences)

Room: Scotiabank Theatre Elastic scattering, a simple process on peripheral reactions, is one of the ideal tools to study the weakly bound nuclei in order to investigate their unusual features [1,2]. A lot of the elastic scattering experiments have been performed for the weakly bound nuclei, such as $^{6}$He [3], $^{11}$Be [4] and $^{11}$Li [5]on heavy targets at the energies around the Coulomb barriers. However, the elastic-scattering data for the proton-halo nuclei above the Coulomb barrier are still scarce. A set of experimental method has been established to measure the differential cross-sections of the elastic scattering on the Radioactive Ion Beam Line in Lanzhou(RIBLL) [6] at the Heavy-Ion Research Facility in Lanzhou(HIRFL) [7]}. Special care was taken to overcome the disadvantages of the broad beam profiles and limited intensities of the radioactive ion beams [8]. The method has been successfully applied to carry out the elastic scattering angular distributions of the proton-rich nuclei $^{8}$B and $^{9,10,11}$C on $^{nat}$Pb target at the energies around 3 times of the Coulomb barrier [9,10]. The experimental data are analyzed using the optical model using a single-folding-type potential and the continuum discretized coupled-channels (CDCC) method. The CDCC calculation describes the angular distribution of $^{8}$B very well. The calculation without taking into account the breakup channel coupling does not differ from that of the full CDCC calculation. That is, the effect of breakup-channel coupling on the elastic scattering is small for $^{8}$B at the energy well above the Coulomb barrier, in contrast to what was observed in the elastic scattering of neutron-rich nuclei on heavy targets at the energies around the Coulomb barrier. The experimental data of $^{9,10,11}$C are analyzed using the optical model with a systematic nucleus-nucleus potential[11]. The experimental data are well described by the optical model calculations. References: [1] N. Keeley et al., Prog. Part. Nucl. Phys. 63 (2009) 396. [2] L. F. Canto et al., Phys. Rep. 596(2015) 1. [3] L. Acosta et al., Phys. Rev. C 84, 044604 (2011). [4] A. Di Pietro et al., Phys. Rev. Lett. 105, 022701 (2010). [5] M. Cubero et al., Phys. Rev. Lett. 109(1997) 262701. [6] Z. Sun et al., Nucl. Instr. and Meth. A 503 (2003) 496 [7] J. W. Xia et al., Nucl. Instr. and Meth. A 488 (2002) 11 [8] Y. Y. Yang et al., Nucl. Instr. and Meth. A 701 (2013) 1 [9] Y. Y. Yang et al., Phys. Rev. C 87 (2013) 044613 [10] Y. Y. Yang et al., Phys. Rev. C 90 (2014) 044606 [11] Y. P. Xu, Phys. Rev. C 87 (2013) 044605

Evolution of collectivity beyond N=60 for Kr isotopes: First spectroscopy of 98,100Kr (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Freddy FLAVIGNY (IPN Orsay)

Room: Scotiabank Theatre Across the nuclear chart, some of the most drastic known shape transitions appear in the A~100 region at N=60 for neutron-rich Zr and Sr isotopes [1,2]. Such a sudden rearrangement of a whole nucleus only adding a couple of nucleons is a peculiar feature of the nuclear system highlighting the subtle interplay between collective and microscopic degrees of freedom which keeps on motivating research efforts since decades. Transitional regions or critical points where this phenomenon happens or disappear are thus preferential areas to be mapped experimentally. Neutron-rich Kr isotopes are especially interesting in this respect since this sudden increase of collectivity at N=60, like in the Zr and Sr chains, was not observed for 96Kr [3]. Instead, a smooth reduction of E(2+1) and rise of B(E2,0+->2+) excitation strength suggest a gradual development of collectivity. Mass measurements of 96Kr, and 98,100Rb isotopes together with charge radii studies also emphasized that this abrupt shape transition at N=60 extends at least up to Z=37 and not to Z=36 in 96Kr but could not rule out that such a transition is not shifted to higher neutron numbers [4,5]. To explore and delineate the boundaries of this nuclear quantum phase transition region [4], we performed the study of very neutron-rich 98,100Kr nuclei during the 2015 SEASTAR campaign using (p,2p) direct reactions from 99,101Rb isotopes at 266 and 257 MeV/u respectively, produced by in-flight fission of 238U. Thanks to the state-of-the-art combination of the RIBF facility, a 100-mm thick liquid hydrogen target and the MINOS+DALI2 setup [6,7], we were able to perform the first in-flight γ-ray spectroscopy of these two isotopes and measure their 2+1 states. The data analysis and the results will be presented and confronted to modern mean-field based theoretical predictions [8]. [1] S. A. E. Johansson, Nucl. Phys 64, 147 (1965). [2] K. Heyde and J. L. Wood, Rev. Mod. Phys. 83, 1467 (2011). [3] M. Albers et al., Phys. Rev. Lett. 108, 062701 (2012). [4] S. Naimi et al., Phys. Rev. Lett. 105, 032502 (2010). [5] V. Manea et al., Phys. Rev. C. 88, 054322 (2013). [6] A. Obertelli et al., Eur. Phys. J. A 50, 8 (2014). [7] S. Takeuchi et al., Nucl. Inst. Meth. A 763, 596 (2014). [8] T. R. Rodriguez, Phys. Rev. C 90, 034306 (2014).

Doppler-shift lifetime measurements in $^{94}$Sr using the TIGRESS integrated plunger (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Aaron Chester (Simon Fraser University)

Room: Scotiabank Theatre Neutron-rich Sr isotopes are characterized by a sudden onset of quadrupole deformation at neutron number $N=60$ demonstrated by the dramatic drop in excitation energy of the first $2^+_1$ state. While theoretical calculations reproduce this onset of deformation qualitatively, they differ in the details of the deformation parameters and excitation energies. Though the emphasis is usually put on the sudden onset of collectivity at $N=60$, it is equally surprising that there is no onset of collectivity when adding up to 8 neutrons beyond the $N=50$ shell closure, which points to an amazing robustness of both the $Z=38$ and $Z=40$ proton (sub)-shell closures. This retardation of the onset of collectivity was first observed by Mach et al. [1] measuring extremely low $B(E2)$ values of $\approx 10$ W.u. in even-even Sr isotopes from $^{90}$Sr to $^{96}$Sr using the fast timing technique. These measurements have an uncertainty of $\approx 40\%$ and are at the limit of the fast timing technique with lifetimes of $\approx 10$~ps; a high precision lifetime measurement in $^{94}$Sr will elucidate whether the onset of collectivity is as sudden as generally assumed. Intense re-accelerated beams delivered by the ISAC-II facility at TRIUMF, Canada's national laboratory for particle and nuclear physics, permit access to nuclear structure information for a wide range of radionuclides via in-beam gamma-ray spectroscopy with TIGRESS, a high-efficiency and Compton-suppressed segmented HPGe array. To take advantage of this opportunity, the TIGRESS Integrated Plunger (TIP) has been constructed at Simon Fraser University [2]. The TIP infrastructure supports Doppler-shift lifetime measurements via the Recoil Distance Method (RDM) using a 24-element TIP CsI(Tl) wall for charged-particle identification. An experiment aimed towards a high-precision ($<10$\%) measurement of the $B(E2,2^+_1\rightarrow 0^+_1)$ reduced transition probability in $^{94}$Sr was performed in December 2015 using inelastic scattering near the Coulomb barrier coupled with an RDM lifetime measurement of a radioactive $^{94}$Sr beam. A Geant4-based code for TIP is being developed as a tool to aid the analysis and for the optimization of future experiments. The device, experimental approach, analysis, and preliminary results will be presented and discussed. This work is presented on behalf of the TIP and TIGRESS collaborations. [1] Mach et al., Nucl. Phys. A 523 (1991) 197. [2] P. Voss et al., Nucl. Inst. and Meth. A 746 (2014) 87.

Single-neutron states and the role of the $\nu$g$_{9/2}$ orbital in $^{71}$Zn (Shell evolution through direct reactions - Spectroscopy of nuclear levels and nuclear shapes through direct reactions)

• Simone Bottoni (Argonne National Laboratory)

Room: Scotiabank Theatre The (high-spin) structure of $^{71}$Zn has been investigated at ATLAS by means of the transfer reaction between heavy ions $^{48}$Ca+$^{70}$Zn at 25$\%$ above the Coulomb barrier, using GRETINA and CHICO-2. In conjunction with Gammasphere data from a similar reaction with a $^{70}$Zn beam on a thick $^{197}$Au target, a level scheme associated with the 3.96 h, 9/2$^+$ isomer in $^{71}$Zn was delineated with the aim to achieve a better understanding of the nature of the neutron excitations close to N = 40. The level sequences built on the g$_{9/2}$ neutron orbital all appear to be of single-particle character. The results will be presented and compared with shell-model calculations using modern effective interactions. Comparisons between the results obtained with the transfer and deep inelastic reactions will also be discussed. Moreover, the present experiment allowed to investigate, for the first time, the feasibility of transfer reactions between heavy ions using GRETINA and it can serve as a benchmark for future experiments. This work is supported by the U.S. Department of Energy, Office of Nuclear Physics, under contract no. DE-AC02-06CH11357 (ANL), DE-AC02-05CH11231 (LBNL, GRETINA), DE-AC52-07NA27344 (LLNL), and NSF.

Investigation of $^{10}$Li resonance component in $^{11}$Li via the $^{11}$Li(p,d) reaction (New instrumentation for direct reaction studies of exotic nuclei)

• Alisher Sanetullaev (Saint Mary's University, TRIUMF, Inha University in Tashkent)

Room: Scotiabank Theatre The unbound system $^{10}$Li is of great interest for the description of the structure of the Borromean neutron halo nucleus $^{11}$Li [1,2]. Borromean neutron halo nuclei are unusual weakly bound states of a core nucleus plus two neutrons. No transfer reaction experiment has been done so far which directly looks at the sub-component $^{10}$Li within $^{11}$Li. While earlier measurements have indicated possible resonances in $^{10}$Li [3-6], it is still not well established which resonance contributes to the ground state configuration of $^{11}$Li and by what spectroscopic factor. To obtain such information a decisive way can be investigating the transfer of one-neutron from $^{11}$Li. The presentation will report observations on $^{10}$Li studied through the first measurement of the p($^{11}$Li,d) one-neutron transfer reaction at beam energy of 6A MeV. This was performed using a solid H2 target at the newly constructed IRIS facility at TRIUMF. The $^{10}$Li residue was populated strongly as a resonance with energy Er = 0.62 ± 0.04 MeV having a total width Γ = 0.33 ± 0.07 MeV. The angular distribution of this resonance is characterized by neutron occupying the 1p1/2 orbital. A DWBA analysis yields a spectroscopic factor of 0.67 ± 0.12 for p1/2 removal strength from the ground state of $^{11}$Li to the region of the peak. The presentation will report observations on $^{10}$Li studied through the first measurement of the p($^{11}$Li,d) one-neutron transfer reaction at beam energy of 6A MeV. This was performed using a solid H2 target at the newly constructed IRIS facility at TRIUMF. The $^{10}$Li residue was populated strongly as a resonance with energy Er = 0.62 ± 0.04 MeV having a total width Γ = 0.33 ± 0.07 MeV. The angular distribution of this resonance is characterized by neutron occupying the 1p1/2 orbital. A DWBA analysis yields a spectro- scopic factor of 0.67 ± 0.12 for p1/2 removal strength from the ground state of $^{11}$Li to the region of the peak. [1] E. Garrido, D.V. Fedorov, A.S. Jensen, Nucl. Phys. A 700 (2002) 117. [2] I. Tanihata, H. Savajols, R. Kanungo, Prog. in Part. and Nucl. Phys. 68 (2013) 215. [3] H.B. Jeppesen, A.M. Moro, U.C. Bergmann, et al., Phys. Lett. B 642 (2006) 449. [4] K.H. Wilcox, R.B. Weisenmiller, G.J. Wozniak, et al., Phys. Lett. B 59 (1975) 142. [5] A.I. Amelin, M.G. Gornov, Yu.B. Gurov, et al., Yad. Fiz. 52 (1990) 1231. [6] M. Zinser, F. Humbert, T. Nilsson, et al., Nuclear Phys. A 619 (1997) 151176.

Locations of breakup in reactions near the fusion barrier (Invited)

• Edward Simpson (Australian National University)

Room: Scotiabank Theatre Above barrier fusion of light, weakly-bound projectiles with heavy targets is known to be suppressed by 25-35% [1-3]. Direct breakup reactions were thought to significantly reduce the probability for fusion of the entire projectile. Transfer reactions populating unbound states in neighbouring nuclei, such as $^5$Li and $^8$Be, have also been found to be a significant trigger of projectile disintegration [4]. Understanding the detail of these processes is crucial [5]: breakup must occur prior to the reactants reaching their mutual barrier in order to suppress fusion. If narrow, long-lived resonances are populated (e.g., $^6$Li 3$^+$ τ≈3×10$^{-20}$ s, $^8$Be 0$^+$ τ≈10$^{-16}$ s), the projectile-like nucleus will remain intact until it reaches the barrier, so cannot suppress fusion. Short lived states (e.g., the $^8$Be 2$^+$) disintegrate more quickly, but with ~10$^{-21}$ s collision timescales their effect on fusion is not yet clear. Here we discuss recent Australian National University measurements of sub-barrier breakup, where absorption of the charged breakup fragments is minimal. We interpret these results using a classical dynamical model [6] that has been extended to account for the energies and lifetimes of resonant states, and discuss what the angular correlations of the fragments may reveal about the location of breakup. [1] M. Dasgupta et al., Phys. Rev. C 66, 041602(R) (2002). [2] Y. W. Wu et al., Phys. Rev. C 68, 044605 (2003). [3] M. Dasgupta et al., Phys. Rev. C 70, 024606 (2004). [4] D. H. Luong et al., Phys. Lett. B 695, 105 (2011); Phys. Rev. C 88, 034609 (2013). [5] E. C. Simpson et al., Phys. Rev. C 93, 024605 (2016) [6] A. Diaz-Torres et al., Phys. Rev. Lett. 98, 152701 (2007).

Scattering of the halo nucleus $^{11}$Be on a heavy target at energies around the Coulomb barrier (Exotic structures through direct reactions)

• María José G. Borge (ISOLDE)

Room: Scotiabank Theatre The discovery of halo nuclei has brought renewed interest in the modelling of nuclear reactions. The dynamics of weakly bound nuclei at energies close to the Coulomb barrier are of great interest due to the interplay between the reaction process and the structure of the projectile. The Coulomb interaction dominates the reaction process with heavy targets, the low binding energy and the strong dipolar polarization contribute to a significant enhancement of the breakup cross section, even below the Coulomb barrier [1]. Besides the one-neutron halo structure and the weak binding energy for the last neutron, $^{11}$Be has one bound excited state at 320 keV (J$^\pi$ = 1/2$^-$) which has a strong dipolar coupling to the gound state (J$^\pi$ = 1/2$^+$). In this conference I will present new experimental data for the elastic, inelastic and breakup channels of the $^{11}$Be+ $^{197}$Au at incident energies around and below the Coulomb barrier, with the elastic and inelastic channels separated for the first time in this energy range [2]. The experiment was performed at TRIUMF, using the HPGe detector array TIGRESS in coincidence with Silicon detectors for the identification of the Be fragments. State-of-the-art CDCC calculations including core excitations are able to explain all the scattering distributions simultaneously, and clearly support the latest dB/dE distribution measured at RIKEN (Fukuda et al [3]). The present study settles the question about the dB/dE to the continuum of the $^{11}$Be and demonstrate that the reaction mechanism is sensitive to subtle structure features, such as core deformation in a halo nucleus. [1] J.P. Fernández-García et al., PRL 110, 142701 (2013) [2] V. Pesudo et al., PRL, submitted. [3] N. Fukuda et al., PRC 70, 054606 (2004)

Study of cluster structure in $^{16}$C via $\alpha$ inelastic scattering (Exotic structures through direct reactions)

• Shunpei KOYAMA (Department of Physics, the University of Tokyo)

Room: Scotiabank Theatre The highly excited states in weakly bound nuclei have recently been attracting considerable interest. In particular, it is important to reveal states with cluster structure which are expected to appear above particle emission threshold energy. On neutron rich nuclei, for example $^{16}$C, such cluster states could decay into both $\alpha$ emission and multi-neutron emission because the $\alpha$ emission threshold energy ($S_\alpha$) is rather higher than those of neutrons. States which decay into $\alpha$ + residual are expected to be preferably clustered. We investigated $\alpha$-cluster states of $^{16}$C by means of invariant mass spectroscopy via $^{12}$Be + $\alpha$ decay channel. We performed an experiment at SAMURAI magnetic spectrometer[1] in RIBF. Secondary $^{16}$C beam with 200 MeV/nucleon was bombarded on cryogenic liquid helium target[2] with thickness of 150 mg/cm$^2$. $^{16}$C was excited via $\alpha$ inelastic scattering, which is one of the effective reactions to populate cluster states above $S_\alpha$[3]. Reaction residues are momentum analyzed by the SAMURAI spectrometer. Coincidence $\gamma$ rays are also tagged by DALI2 $\gamma$-ray detector array surrounding the target. Energy levels of $^{16}$C above $S_\alpha$ are reconstructed from four momenta of $^{12}$Be and $\alpha$ residues and detected $\gamma$-ray energy. Several levels are identified. We will report the experimental result and discuss it by comparison with levels given by an AMD calculation[4]. [1] T. Kobayashi, et. al., Nucl. Instr. and Meth. B317 (2013) 294. [2] M. Kurata-Nishimura, et. al., RIKEN Accel. Prog. Rep. 46 (2013) 165. [3] T. Kawabata, et. al., Phys. Lett. B 646 (2007) 6. [4] T. Baba, Y. Chiba and M. Kimura, Phys. Rev. C 90 (2014) 064319.

Probing nuclear properties of imbalanced Fermi systems with quasi-free proton knockout reactions (Theoretical developments of direct reactions)

• Sam Stevens (Department of Physics and Astronomy, Ghent University, Belgium)

Room: Scotiabank Theatre We have developed a reaction model for quasi-free A(p, pN)B reactions with unstable nuclei. This model makes it possible to connect experimental data from (p, pN) measurements in inverse kinematics at radioactive-beam facilities [1], to the mean-field properties of imbalanced nuclei (spectroscopic factors and single-particle wave functions). The cross sections are calculated in a factorised way, following the approach developed in Refs. [2] and [3]. The general idea is to calculate the hard scattering part as a free pN scattering cross section with a phase-space correction, multiplied by the momentum probability distribution for the struck nucleon. The effect of soft interactions with the spectator nucleons is accounted for by using a Relativistic Multiple Scattering Glauber Approximation (RMSGA) [3]. A semi-classical approximation accounts for the effect of single-charge exchange [4]. The RMSGA [5] is based on the eikonal approximation and uses free nucleon-nucleon scattering cross sections to calculate the attenuation. The (p, pN) model has been tested against momentum distributions obtained at the HIMAC accelerator in the National Institute of Radiological Sciences in Chiba, Japan [6]. Short-range correlations (SRC) in imbalanced nuclei are highly interesting manifestations of beyond-mean-field properties. They can be experimentally probed with two-nucleon knockout reactions by selecting the appropriate kinematics. We have developed a reaction model for proton-induced SRC-driven two-nucleon knockout reactions A(p, pNN)B with unstable nuclei. The model is based on the factorization properties that have been confirmed in SRCdriven A(e, e0NN) reactions [4, 7, 8]. Estimates of the expected cross sections for SRC-driven two-nucleon knockout reactions with unstable nuclei will be presented. [1] T. Aumann, Prog. Part. Nucl. Phys. 59 (2007) 3. [2] T. Aumann, C.A. Bertulani and J. Ryckebusch, Phys. Rev. C 88 (2013) 064610. [3] B. Van Overmeire, W. Cosyn, P. Lava, and J. Ryckebusch, Phys. Rev. C 73 (2006) 064603. [4] C. Colle, W. Cosyn, J. Ryckebusch, and M. Vanhalst, Phys. Rev. C 89 (2014) 024603. [5] W. Cosyn, M. C. Martin´ez, and J. Ryckebusch, Phys. Rev. C 77 (2008) 034602. [6] T. Kobayashi, K. Ozeki, K. Watanabe, Y. Matsuda, Y. Seki, T. Shinohara, T. Miki and Y. Naoi et al., Nucl. Phys. A 805 (2008) 431. [7] J. Ryckebusch, Phys. Lett. B 383 (1996) 1. [8] C. Colle, W. Cosyn, J. Ryckebusch, arXiv:1512.07841 [nucl-th].

Transfer to the continuum calculations of quasifree (p,pn) and (p,2p) reactions (Theoretical developments of direct reactions)

• Mario Gomez-Ramos (Universidad de Sevilla)

Room: Scotiabank Theatre Nucleon removal (p,pn) and (p,2p) reactions at intermediate energies have gained renewed attention in recent years as a tool to extract information from exotic nuclei, thanks to the availability of exotic beams with which to perform these reactions in inverse kinematics. The information obtained from these experiments is complementary to that obtained from nucleon removal experiments with heavier targets (knockout), but is expected to be sensitive to deeper portions of the wave function of the removed nucleon. In this contribution, we present calculations for (p,2p) and (p,pn) reactions performed within the transfer to the continuum method [Phys. Rev. C **92**, 044605]. This is a fully quantum-mechanical formalism, based on the application of the prior form transition amplitude, in which the 3-body final states are expanded in a discretized basis of p-N continuum states. This method is expected to be suitable for the analysis of observables of inclusive nature which are currently under study in the experiments performed at GSI and RIKEN. Results for different nuclei are presented, employing Reid Soft-Core nucleon-nucleon interaction for the interaction between the incoming proton and the extracted nucleon and either JLM potentials or microscopic nucleus-nucleon potentials calculated by folding the effective Paris-Hamburg g-matrix NN interaction with Hartree-Fock densities for the entrance and exit channels, depending on the range of energies studied. In the case of (p,pn) reactions, special interest is devoted to the (p,d) channel, which can be treated on equal footing to quasi-free scattering channels within the transfer to the continuum formalism and may compete with them, specially at energies below $100$ MeV per nucleon.

Study of one- and two-neutron removal reactions with core + n + n model (Theoretical developments of direct reactions)

• Takuma Matsumoto (Kyushu University)

Room: Scotiabank Theatre Neutron-rich nuclei have exotic properties such as halo, skin formations and shell evolution. Study of these properties is one of the main subject in nuclear physics. Neutron removal reactions have played a key role in the study. Spectroscopic factors and orbital angular momenta of valence nucleons in incident nuclei can be deduced from the removal cross sections. To understand the exotic properties of neutron-rich nuclei, an accurate analysis for neutron removal reactions is highly desired. As one of a reliable method of describing removal processes, the eikonal reaction theory (ERT) has been proposed [1]. ERT is a method of calculating one- and two-neutron removal reactions at intermediate incident energies. In ERT, Coulomb breakup is treated accurately with the continuum discretized coupled-channels method [2], which has been successful for describing breakup processes of two- and three-body projectiles. In this study, we analyze neutron removal reactions with the eikonal reaction theory, where neutron rich nuclei are described by core + valence neutrons in order to treat accurately a pairing correlation of valence neutrons. The pairing correlation is significant for construction of halo and shell evolution. In the presentation, we will discuss the exotic properties of neutron rich nuclei of Be- and C- isotopes especially. [1] M. Yahiro, K. Ogata, and K. Minomo, Prog. Theor. Phys. 126, 167 (2011). [2] M. Yahiro K. Ogata, T. Matsumoto and K. Minomo, Prog. Theor. Exp. Phys. 2012, 01A206 (2012).

A candidate for linear-chain $\alpha$ clustering in $^{14}$C (Exotic structures through direct reactions)

• Saul Beceiro-Novo (Michigan State University)

Room: Scotiabank Theatre The existence of exotic nuclei with $\alpha$-cluster structure has been described by several theoretical models. However, experimental data are needed to constrain these model predictions. In particular, the one-dimensional alignment of multiple $\alpha$ particles known as linear-chain structure has been highly elusive experimentally. The capabilities of the Prototype Active-Target Time-Projection Chamber (PAT-TPC) allows one to measure charged-particle decays with very low-energy thresholds and a high efficiency due to its thick gaseous active target volume. Thus, it is well suited to search for low-energy $\alpha$-cluster reactions. Radioactive-ion beams produced by the *TwinSol* facility at the University of Notre Dame were delivered to the PAT-TPC to study resonant elastic and inelastic $\alpha$ scattering of a radioactive $^{10}$Be beam that excited states in the neutron-rich nucleus $^{14}$C. Differential cross sections and excitation functions were measured. The good quantitative agreement with recent predictions by an antisymmetrized molecular dynamics model makes the 2$^+$ and 4$^+$ states observed excellent candidates for linear $\alpha$ structure states in $^{14}$C.

Non-stationary approach to description of neutron transfer in reactions with $^{3,6,8}$He nuclei (Theoretical developments of direct reactions)

• Viacheslav Samarin (Joint Institute for Nuclear Research)

Room: Scotiabank Theatre Experimental cross sections for formation of isotopes $^{44,46}$Sc in reactions $^{3,6}$He+ $^{45}$Sc [1,2], $^{65}$Zn in reaction $^{6}$He+ $^{64}$Zn [3] and $^{196,198}$Au in reactions $^{3,6,8}$He+$^{197}$Au [4-6] have been analyzed. To calculate neutron transfer probabilities and cross sections the time-dependent Schrödinger equation (TDSE) [7,8] for external neutrons of $^{3,6,8}$He and target nuclei has been solved numerically. The contribution of fusion-evaporation processes to the experimental data has been taken into account within the statistical model. The results of calculation demonstrate overall satisfactory agreement with experimental data. References 1. N. K. Skobelev *et al*., Phys. Part. and Nucl. Lett. **10**, 410 (2013). 2. N. K. Skobelev *et al*., J. Phys. G **38**, 035106 (2011). 3. V. Scuderi *et al*., Phys. Rev. C **84**, 064604 (2011). 4. N. K. Skobelev *et al*., Phys. Part. and Nucl. Lett. **11**, 114 (2014). 5. Yu. E. Penionzhkevich *et al*., Eur. Phys. J. A **31**, 185 (2007). 6. A. Lemasson *et al*. Phys. Lett. B **697**, 454 (2011). 7. V. V. Samarin, Phys. of Atom. Nucl. **78**, 128 (2015). 8. V. V.Samarin, EPJ Web Conf. **86**, 00040 (2015).