PIONS IN THE NUCLEAR MEDIUM AND DRELL-YAN SCATTERING

We investigate the modification of the pion cloud in the nuclear mediu m and its effect on the nuclear Drell-Yan process. The pion's in-mediu m self-energy is calculated in a self-consistent delta-hole model, wit h particle-hole contributions also included. Both the imaginary and re al parts of the pion's and delta's self-energy are taken into account and related through a dispersion relation assuring causality. The resu lting in-medium pion light-cone momentum distribution shows only a sli ght enhancement compared to the one of the free nucleon. As a conseque nce the ratio of the cross section for Drell-Yan scattering on nuclear matter and nucleonic targets is close to unity, in agreement with exp eriment.