No abstract

The isobar-doorway model for pion-nucleus interaction is extended to coherent n' photoproduction. The modifications to the transition operator due to many-body effects are shown to be the same as those in the optical potential. Nonlocality associated with isobar propagation, recoil corrections, and an off-shell extrapolation of the n. Nd vertex are included. The calculated cross sections are found to be in good agreement with the existing data.NUCLEAR REACTIONS Coherent 7t photoproduction; isobar doorway; optical potential model. Many-body modifications of the transition operator.

The pion-nucleus optical potential in the isobar-doorway model is extended to isospin nonzero nuclei.Many-body efFects. in isobar propagation are parametrized in terms of an energy shift and width and an isobar nonlocality. Isospin dependence of these parameters is found to play an important role in determining pion charge exchange cross sections.NUCLEAR REACTIONS Pion charge exchange, isobar-doorway optical potential model, isospin-dependent modification of isobar propagator.The isobar-doorway model provides a convenient framework in which to parametrize the pionnucleus optical potential. This was done in Ref. 1 where elastic scattering from isospin zero nuclei was discussed. In this paper we extend the isobar-doorway optical potential to nonzero isospin and calculate cross sections for single and double pion charge exchange in the resonance region.In an earlier paper' we showed that the (m', &) total cross section depends very sensitively on the choice of energy for the elementary pionnucleon t-matrix in a factorized first-order optical potential description. Here we discuss this effect from the point of view of isobar propagation.Using isospin invariance the single and double charge exchange amplitudes to isobaric analog states can be written as i 0+ = )

No abstract

No abstract