INCLUSIVE (GAMMA, PI) REACTIONS IN NUCLEI

The double-differential cross section for inclusive (gamma, pi) reactions in nuclei is studied by combining elements of microscopic many-body theories previously developed. Pion production in nuclei changes with respect to the impulse approximation not only because of nuclear modifications to the primary (gamma, pi) reaction compared to the free case, but mostly due to the final-state interaction of the pions. The multiple collisions of the pions change their direction, energy and charge. On the other hand, pion absorption drastically reduces the number of emerging pions with respect to those originally produced, giving rise to a source of photon absorption which we call indirect and dominates this cross section for heavy nuclei. We separate direct and indirect photoabsorption and show that the latter grows faster than A, thus being more sensitive to details of pion absorption than pionic reactions themselves. These magnitudes have not yet been measured and we stress the importance of carrying out that separation as well as looking at other details of the photonuclear reaction. Comparison with existing (gamma, pi) data is also done.