Selectivity of the one-neutron knockout reaction on Cl 45 and the collapse of the N = 28 shell closure

Neutron hole states in the exotic N=27 isotope {sup 44}Cl have been populated using the intermediate-energy single-neutron knockout reaction {sup 9}Be({sup 45}Cl,{sup 44}Cl)X. The momentum distribution of the residual {sup 44}Cl nuclei after direct population of the ground state is consistent with removal of an l=1 neutron. This observation and comparison with a shell-model calculation imply that p{sub 3/2} neutrons from above the N=28 major shell closure play important roles in the ground states of both {sup 44}Cl and {sup 45}Cl. The present result is significant because {sup 44}Cl is even closer to the valley of stability than {sup 43}S, where a similar result was recently obtained using a g-factor measurement.