A microscopic calculation of photoabsorption cross sections on protons and nuclei

A recently developed model for p-meson propagation in dense hadronic matter is applied to total photoabsorption cross sections in gamma-proton and gamma-nucleus reactions. Within the vector dominance model the photon coupling to the virtual pion cloud of the nucleon, two-body meson-exchange currents, as well as gamma-nucleon resonances are included. Whereas the gamma p reaction is determined by the low-density limit of the model, higher orders in the nuclear density are important to correctly account for the experimental spectra observed on both light and heavy nuclei over a wide range of photon energies, including the region below the pion threshold. in connection with soft dilepton spectra in high-energy heavy-ion collisions we emphasize the importance of photoabsorption to further constrain the parameters of the model. (C) 1998 Elsevier Science B.V.