Photoproduction of $\pi^+4p$-pairs on the $^{16}$O nucleus and isobar configurations

The yield of the $^{16}$O$(\gamma,\pi^+ p)$ reaction has been measured in the region of the excitation of the $\Delta$(1232) isobar at high momentum transfers to the residual nuclear system. The experimental data are interpreted within the model taking into account manifestations of isobar configurations in the ground state of the $^{16}$O nucleus. Direct and exchange mechanisms of the production of pions with emission of one and two nucleons, which follow from the structures of the density matrices for these reactions, have been considered. The probability of the production of the $\Delta$-isobar in the ground state of the $^{16}$O nucleus has been empirically estimated as $P_\Delta = 0.019 \pm 0.003 \pm 0.003$.