Effective interaction for 16O(p,p') at Ep=318 MeV.

Abstract

We report new cross-section and analyzing power data for the excitation by 318 MeV protons of 20 states of $^{16}\mathrm{O}$ below 14 MeV. The data for normal-parity isoscalar excitations are compared with calculations based upon the nonrelativistic impulse approximation using both density-independent and density-dependent interactions in the local-density approximation. These comparisons clearly indicate that density-dependent modifications of the effective interaction are required. Although the Paris-Hamburg, Nakayama-Love, and Ray interactions all predict significant medium modifications, none describes the data particularly well. Therefore, we fitted an empirical effective interaction to the data for five inelastic transitions simultaneously using a self-consistency cycle that maintains consistency between transition potentials and microscopic distorting potentials. This interaction describes the inelastic data as well as elastic data and data for $^{40}\mathrm{Ca}$ which were not included in the fitting procedure. Therefore, the local-density approximation is supported by the phenomenology. However, medium modifications of the effective interaction are substantially stronger than predicted and persist to low density. The optical potentials are similar to the Schr\"odinger-equivalent potentials from the relativistic IA2 model, showing that the equivalent density dependence due to virtual NN\ifmmode\bar\else\textasciimacron\fi{} pairs is comparable to the short-range repulsion fitted to inelastic-scattering data.