A search for unexpected bound states in $^{15}$B

Bound states in $^{15}$B are to be populated through the one proton removal reaction from a $^{16}$C beam produced at the RCNP EN Course through $^{18}$O fragmentation. $\gamma$-decays from these states will be identified by an array of Compton-suppressed HPGe Clover detectors (CAGRA). The goals consist of i) identifying any previously unobserved and unexpected bound states in $^{15}$B and ii) to assign total angular momenta to known excited states for the first time. At present only two bound states have been observed in $^{15}$B, neither with firm spin or parity assignments [1]. The present work to be discussed is aimed at determining whether an excited 3/2$^-$ state, a state with identical spin-parity as the ground state, resides below the neutron separation energy in $^{15}$B. Such an excited $3/2^-$ state is not predicted to appear below the $^{15}$B $S_n$ by shell-model calculations using various $p$-$sd$ interactions. However, a robust systematic, probably related to the $s$-wave trends found in the single-neutron states in this region [2], has been observed for neutron-rich $N$=10 nuclei and it suggests that the state may appear lower in excitation energy than expected. Providing some measure of validation for the $N$=10 prediction is a similar trend noticed in the energy differences between ground ($p$)$^{2}$ neutron states and excited ($sd$)$^2$ neutron states in the $N$=8 neutron-rich isotones [3]. In addition to a search for this unexpected state, additional spectroscopic information on $^{15}$B will better aid in the understanding of the $N$=10 isotones when transitioning from $^{16}$C into sparsely probed $^{14}$Be. Details of the experimental procedures and motivation will be presented and discussed.\\[4pt] [1] Y. Kondo, T. Nakamura, N. Aoi et al., Phys. Rev. C 71, 044611 (2005).\\[0pt] [2] C. R. Hoffman, B. P. Kay, J. P. Schiffer, Phys. Rev. C 89, 061305(R) (2014).\\[0pt] [3] H. Iwasaki, A. Dewald, C. Fransen et al., Phys. Rev. Lett. 102, 202502 (2009)