Higher Nucleon Resonances in Exclusive $(\gamma, \pi N)$ Reactions on Nuclei

Abstract

We report calculations for exclusive pion photoproduction on nuclei beyond the first resonance region in the distorted wave impulse approximation. The elementary operator contains contributions from the resonances $P_{33}(1232)$, $P_{11}(1440)$, $D_{13}(1520)$, $D_{33}(1740)$, $S_{11}(1535)$, $S_{11}(1650)$, and $F_{15}(1680)$, in addition to the usual Born plus vector meson contributions. It gives a good description of single pion photoproduction data up to about 1.1 GeV. Final state interactions are incorporated via optical potentials and are found to be substantial in the coincidence cross sections, but insensitive to the photon asymmetry. Clear signatures of possible medium modifications of the $D_{13}$ and $F_{15}$ resonances are predicted.