Pion photoproduction on nucleus with two-nucleon emission

Abstract

A model for the pion photoproduction on nuclei in the A (γ, πNN ) B reaction is presented. This is an extension of our recent model for the A (γ, πN ) B reaction. In this approach we have moved beyond the standard shell-model considering ∆N correlations in the nuclear wave functions, which are caused by the virtual transitions NN → ∆N → NN in the ground state of the nucleus. The main ingredients of the model are the two-and threeparticle density matrices and the transition operators γ∆ → Nπ and γN → Nπ. The direct and exchange reaction mechanisms, which follow from the structure of the density matrices, are examined. The model is used to investigate the 12 C(γ, π + p) and 12 C(γ, π − p) reactions in the kinematic region of the large momentum transfers to the residual nuclear system, where the pion production occurs with the emission of two nucleons.