Unbound states in $^{17}$C and $p-sd$ shell-model interactions
Résumé
Unbound states in were investigated via one-neutron removal from a beam at an energy of 245 MeV/nucleon on a carbon target. The energy spectrum of , above the single-neutron decay threshold, was reconstructed using invariant mass spectroscopy from the measured momenta of the fragment and neutron, and was found to exhibit resonances at =0.52(2), 0.77(2), 1.36(1), 1.91(1), 2.22(3) and 3.20(1) MeV. The resonance at =0.77(2) MeV [=1.51(3) MeV] was provisionally assigned as the second state. The two resonances at =1.91(1) and 3.20(1) MeV [=2.65(2) and 3.94(2) MeV] were identified, through comparison of the energies, cross sections and momentum distributions with shell-model and eikonal reaction calculations, as p-shell hole states with spin-parities and , respectively. A detailed comparison was made with the results obtained using a range of shell-model interactions. The YSOX shell-model Hamiltonian, the cross-shell part of which is based on the monopole-based universal interaction, was found to provide a very good description of the present results and those for the neighbouring odd-A carbon isotopes – in particular for the negative parity cross-shell states.