On the mechanism of the photoproduction of pion-nucleon pairs on nuclei

The data from an experiment performed at the MAMI accelerator in Maintz in which the differential cross sections for the photoproduction of positive pions on the carbon nucleus accompanied by the emission of nucleons have been analyzed. The behavior of the experimental cross sections as functions of the pion energy and nucleon emission angle, which cannot be explained in the quasi-free approximation, is interpreted in a model where an intermediate quasi-bound isobar nuclear state is formed and decays with the emission of a pion and a nucleon.