Testing microscopic medium effects on nucleons and mesons using polarization observables in high-spin, unnatural-parity(p→,p′)reactions at 200 MeV

Abstract

We compare measurements of the cross section, analyzing power, induced polarization, and polarization transfer coefficients for $(\stackrel{\ensuremath{\rightarrow}}{p},{p}^{\ensuremath{'}})$ reactions leading to unnatural-parity, high-spin states in ${}^{16}\mathrm{O}$ and ${}^{28}\mathrm{Si}$ with distorted wave impulse approximation calculations. We use an effective nucleon-nucleon (NN) interaction obtained from a microscopic treatment of nuclear medium effects. The NN potential is generated from a one-boson-exchange model of the nuclear force that reproduces NN scattering data well. Medium effects are incorporated through a G matrix obtained within a Dirac-Brueckner approach to nuclear matter. While agreement for some observables is good, differences for the polarization transfer coefficients indicate that systematic problems with the relative sizes of the spin-orbit and tensor interaction components exist. The differences are larger for ${}^{28}\mathrm{Si}$ than for ${}^{16}\mathrm{O}.$ A new model that incorporates density-dependent meson mass reductions produces only small effects that do not change the quality of the agreement. Connections to previous calculations are investigated.