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

Coherent pi(0) photo- and electroproduction on He-4 and C-12 nuclei is inve stigated in the framework of a distorted wave impulse approximation in mome ntum space. The elementary process is described by the recently developed u nitary isobar model. Medium effects are considered by introducing a phenome nological Delta self-energy. Recent experimental data for He-4 and C-12 can be well described over a wide range of energies and emission angles by the assumption that the Delta-nuclear interaction saturates. (C) 1999 Elsevier Science B.V. All rights reserved.