First evidence for a virtual 18B ground state

Abstract The decay of the neutron unbound ground state of 18 B was studied for the first time through a single-proton knockout reaction from a 62 MeV/u 19 C beam. The decay energy spectrum was reconstructed from coincidence measurements between the emitted neutron and the 17 B fragment using the MoNA/Sweeper setup. An s -wave line shape was used to describe the experimental spectrum resulting in an upper limit for the scattering length of − 50 fm which corresponds to a decay energy s -wave decay of 18 B provides an experimental verification that the ground state of 19 C includes a large s -wave component. The presence of this s -wave component shows that s – d mixing is still present in 18 B and that the s 1 / 2 orbital has not moved significantly below the d 5 / 2 orbital.