Photoproduction of charged pions on neutrons. II

Abstract

A comprehensive theory is developed for photoproduction of charged pions on bound neutrons in deuterons taking into consideration the effects of off-energy-shell amplitudes, Fermi motion, the D state and the Pauli exclusion principle. The authors point out primarily that there are two basic gamma N to pi N amplitudes, generally at two different energies in the respective pi N centre-of-mass (CM) frames, which contribute to the reaction gamma d to pi +or-NN and that both these amplitudes are necessarily off the energy shell. Following the prescription generally used that the off-energy-shell photoproduction amplitudes could be taken to be the same as the on-energy-shell amplitudes at an effective photon energy different from the energy of the beam, the authors investigate how the differential cross section, the pi -/ pi + ratio, the photon polarisation asymmetry, the recoil proton polarisation and the target asymmetry are sensitive to the precise inclusion of the exchange amplitudes. The effect of the D-state contributions on the polarisation and the asymmetries are also studied. The nature of the approximations involved in the existing formulae in the literature are also clearly brought out by showing that they follow from these results on making various simplifying assumptions.