Reduction of spectroscopic overlap across the Z=8 shell in neutron-rich nuclei

The recent discovery and spectroscopic measurements of O27 and O28 suggests the disappearance of the N=20 shell structure in these neutron-rich oxygen isotopes. We measured one- and two-proton removal cross sections from F27 and Ne29, respectively, extracting spectroscopic factors and comparing them to shell model overlap functions coupled with eikonal reaction model calculations. The invariant mass technique was used to reconstruct the two-body (O24+n) and three-body (O24+2n) decay energies from knockout reactions of F27 (106.2 MeV/u) and Ne29 (112.8 MeV/u) beams impinging on a Be9 target. The one-proton removal from F27 strongly populated the ground state of O26 and the extracted cross section of 3.4−1.5+0.3 mb agrees with eikonal model calculations that are normalized by the shell model spectroscopic factors and account for the systematic reduction factor observed for single nucleon removal reactions within the models used. For the two-proton removal reaction from Ne29 an upper limit of 0.08 mb was extracted for populating states in O27 decaying though the ground state of O26. The measured upper limit for the population of the ground state of O26 in the two-proton removal reaction from Ne29 indicates a significant difference in the underlying nuclear structure of F27 and Ne29.Published by the American Physical Society2024