D5/2proton hole strength in neutron-richP43: Shell structure and nuclear shapes nearN=28

Abstract

We report on the use of the one-proton knockout reaction from $^{44}\mathrm{S}$ to determine the location of ${d}_{5/2}$ proton strength in neutron-rich $^{43}\mathrm{P}$. The results are used to test two shell-model frameworks with different pictures of the evolution of single-proton energies along the $N=28$ isotones near the neutron dripline. We observe a concentration of ${d}_{5/2}$ proton hole strength near 1 MeV in excitation energy. This result favors the recent shell-model interaction of Utsuno et al. [Eur. Phys. J. Spec. Top. 150, 187 (2007)] and provides additional evidence for an oblate shape for $^{42}\mathrm{Si}$.