Empirical density-dependent effective interaction for nucleon-nucleus scattering at 500 MeV

We report new cross-section and analyzing-power data for the excitation by 498-MeV protons of all narrow normal-parity states of {sup 16}O below 12.1-MeV excitation. In addition, spin-rotation measurements for elastic scattering and depolarization measurements for the 1{sub 1}{sup {minus}}, 2{sub 1}{sup +}, and 3{sub 1}{sup {minus}} states of {sup 16}O have been performed. These data are used in conjunction with existing data for {sup 40}Ca to study medium corrections to the effective interaction for nucleon-nucleus scattering at 500 MeV. Systematic differences between the data and nonrelativistic impulse approximation calculations based upon either the free {ital t} matrix or a recent density-dependent effective interaction are interpreted within the framework of the local-density approximation. An empirical effective interaction has been constructed which parametrizes the density dependence of the medium modifications in a simple form amenable to phenomenological analysis of data.