Asymmetry dependence of nucleon correlations in spherical nuclei extracted from a dispersive-optical-model analysis

Neutron elastic-scattering angular distributions were measured at beam energies of 11.9 and 16.9 MeV on Ca-40,Ca-48 targets. These data plus other elastic-scattering measurements, total and reaction cross-sections measurements, (e, e' p) data, and single-particle energies for magic and doubly magic nuclei have been analyzed in the dispersive optical-model (DOM), generating nucleon self-energies (optical-model potentials) that can be related, via the many-body Dyson equation, to spectroscopic factors and occupation probabilities. It is found that, for stable nuclei with N >= Z, the imaginary surface potential for protons exhibits a strong dependence on the neutron-proton asymmetry. This result leads to a more modest dependence of the spectroscopic factors on asymmetry. The measured data and the DOM analysis of all considered nuclei clearly demonstrate that the neutron imaginary surface potential displays very little dependence on the neutron-proton asymmetry for nuclei near stability (N >= Z).