Photoreactions on Nuclei and Vector-Meson-Dominance Breaking

Within a coupled-channel optical model, calculations of photon-nucleus total cross sections and π⁺ photoproduction on nuclei at high energy are presented and compared with experimental data. The question of the validity of vector-meson dominance (VMD) is discussed. It is found that the fair agreement between theory and experiment in a recent paper by Bochmann, Margolis, and Tang can be greatly improved if one uses experimental two-body amplitudes and allows for deviations from the VMD model for the production reactions γp-->ρ⁰p and γp-->π⁺n.