Photoproduction of Neutral Pions from Complex Nuclei

Abstract

The photoproduction of neutral pions from complex nuclei is expressed in terms of the production amplitudes from single nucleons, as well as certain properties of the nuclear ground state. Methods are developed for the evaluation of the nuclear matrix elements. Correlations between nucleons lead to suppression of the incoherent cross section for small momentum transfers. The coherent nuclear production is strongly peaked at an angle $\ensuremath{\theta}\ensuremath{\approx}\frac{2}{\mathrm{kR}}$. Pions can also be produced by the coupling of the incident photon with the nuclear Coulomb field. The cross section for this process is peaked at an angle $\ensuremath{\theta}\ensuremath{\approx}\frac{{{m}_{\ensuremath{\pi}}}^{2}}{2{k}^{2}}$. Final-state interactions of the produced pion are included by means of the Fernbach-Serber-Taylor model. This leads to attenuation of the nuclear production and to a change in shape of the Coulomb production. The theoretical predictions are compared with experimental measurements at 250 and 900 MeV.