First evidence for a virtual 18B ground state

摘要

The decay of the neutron unbound ground state of18B was studied for the first time through a single-proton knockout reaction from a 62 MeV/u19C beam. The decay energy spectrum was reconstructed from coincidence measurements between the emitted neutron and the17B fragment using the MoNA/Sweeper setup. Ans-wave line shape was used to describe the experimental spectrum resulting in an upper limit for the scattering length of?50fmwhich corresponds to a decay energy <10 keV. Observing ans-wave decay of18B provides an experimental verification that the ground state of19C includes a larges-wave component. The presence of thiss-wave component shows thats–dmixing is still present in18B and that thes1/2orbital has not moved significantly below thed5/2orbital.