Photoreactions on Nuclei and Vector-Meson-Dominance Breaking

Abstract

Within a coupled-channel optical model, calculations of photon-nucleus total cross sections and ${\ensuremath{\pi}}^{+}$ 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 $\ensuremath{\gamma}p\ensuremath{\rightarrow}{\ensuremath{\rho}}^{0}p$ and $\ensuremath{\gamma}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}n$.