PHOTOPRODUCTION OF VECTOR-MESONS OFF NUCLEONS NEAR-THRESHOLD

We propose a simple meson-exchange model of the photoproduction of rho - and omega-mesons off protons near threshold (E(gamma) less than or s imilar to 2 GeV). This model provides a good description of the availa ble data and implies a large rho-nuclxeon interaction in the scalar ch annel (sigma-exchange). We use this phenomenological interaction to es timate the leading contribution to the self-energy of rho-mesons in ma tter. The implications of our calculation for experimental studies of the rho-meson mass in nuclei are discussed.