Thresholdπ0photoproduction from complex nuclear targets

The photoproduction of neutral pions near threshold from complex nuclear targets in investigated. Momentum dependent terms in the photoproduction operator and a two-nucleon charge exchange production mechanism are included. Various selection rules related to the quantum numbers of the nuclear states involved are discussed. Differential cross sections for pion energies ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ are calculated using realistic shell model wave functions. The effects of distortion of the pion wave function are found to be small, but the two-nucleon charge exchange mechanism is found to dominate the coherent production from $J\ne 0$ targets near threshold.