Medium effects in coherent pion photo- and electroproduction on 4He and 12C

Coherent π0 photo- and electroproduction on 4He and 12C nuclei is investigated in the framework of a distorted wave impulse approximation in momentum space. The elementary process is described by the recently developed unitary isobar model. Medium effects are considered by introducing a phenomenological Δ self-energy. Recent experimental data for 4He and 12C can be well described over a wide range of energies and emission angles by the assumption that the Δ-nuclear interaction saturates