MEDIUM EFFECTS IN THE PRODUCTION AND DECAY OF VECTOR-MESONS IN PION-NUCLEUS REACTIONS

The omega-, rho-, and phi-resonance production and their dileptonic de cay in pi(-)A reactions at 1.1-1.7 GeV/c are calculated within the int ranuclear cascade (INC) approach. The invariant mass distribution of t he dilepton pair for each resonance can be decomposed in two component s which correspond to their decay ''inside'' the target nucleus and in the vacuum, respectively. The first components are strongly distorted by the nuclear medium due to resonance-nucleon scattering and a possi ble mass shift at finite baryon density. These medium modifications ar e compared to background sources in the dilepton spectrum from pi N br emsstrahlung as well as the Dalitz decays of omega and eta mesons prod uced in the reaction, Detailed predictions for pi(-)Pb reactions at 1. 3 and 1.7 GeV/c are made within several momentum bins for the lepton p air. (C) 1997 Elsevier Science B.V.