Description of initial-and final-state-interaction effects for the reaction γp → π−Δ++ in the region of nucleon-resonance excitation

Abstract

A model has been developed for describing the cross section for the reaction γr,vp → π−Δ++ in the energy region of nucleon-resonance excitation, and relevant calculations have been performed. The model takes into account the contribution of all reliably established resonances with masses less than 2 GeV and the contributions of nonresonance mechanisms in the approximation of Born diagrams. On the basis of data on the amplitudes of pion-nucleon interactions, a method has been evolved for phenomenologically describing the coupling of initial and final states with open inelastic channels. Calculations performed in this study represent a first step in developing a method for determining the electromagnetic form factors for nucleon resonances in exclusive reactions of pion-pair production on a nucleon by real and virtual photons.