Spectator isobar production in the $A\left( {\gamma ,\pi NN} \right)B$ reaction

We present an analysis of the spectator mechanism of $\Delta$-isobar production in the pion photoproduction on nuclei with the emission of two nucleons. The reaction mechanism is studied within the framework of the $\Delta N$-correlation model, which considers the isobar and nucleon of the $\Delta N$-system produced in the nucleus at the virtual $NN \to \Delta N$ transition, to be in a dynamic relationship. The two-particle transition operator for nuclei is obtained by the \textit{S}-matrix approach. We consider the properties of the spectator mechanism of isobar production using the example of the reaction $^{16}$O$(\gamma ,\ \pi ^{ - }pn)^{14}$O. Numerical estimates of the cross section are obtained in the kinematic region, where it is possible to expect the manifestation of bound isobar-nuclear states.