Unbound states in 17C and p-sd shell-model interactions

Unbound states in 17C were investigated via one-neutron removal from a 18C beam at an energy of 245 MeV/nucleon on a carbon target. The energy spectrum of 17C, above the single-neutron decay threshold, was reconstructed using invariant mass spectroscopy from the measured momenta of the 16C fragment and neutron, and was found to exhibit resonances at Er=0.52(2), 0.77(2), 1.36(1), 1.91(1), 2.22(3) and 3.20(1) MeV. The resonance at Er=0.77(2) MeV [Ex=1.51(3) MeV] was provisionally assigned as the second 5/2+ state. The two resonances at Er=1.91(1) and 3.20(1) MeV [Ex=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 1/2-1 and 3/2-1 , 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 monopolebased 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. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP3.

Automated summary

Unbound states in 17C were studied by removing one neutron from an 18C beam at an energy of 245 MeV/nucleon on a carbon target. The energy spectrum of 17C above the single-neutron decay threshold was reconstructed using invariant mass spectroscopy, revealing resonances at 0.52(2), 0.77(2), 1.36(1), 1.91(1), 2.22(3), and 3.20(1) MeV. Through comparisons with calculations, the resonance at 0.77(2) MeV was tentatively assigned as the second 5/2+ state, while the resonances at 1.91(1) and 3.20(1) MeV were identified as p-shell hole states with spin-parities 1/2-1 and 3/2-1, respectively. A YSOX shell-model Hamiltonian based on the monopole-based universal interaction provided a good description of the results.