COHERENT TWO PION PHOTOPRODUCTION ON C-12

摘要

We develop the formalism for coherent two pion photoproduction in nuclei and perform actual calculations of cross sections for pi(-)pi(+) and pi(0) pi(0) photoproduction on C-12. We find that due to the isospin symmetry the cross section for pi(0) pi(0) production is very small and has a maximum when the pions propagate together. However, the kinematical region where the energies and polar angles of the two pi(0) mesons are equal and their relative azimuthal angle phi = 180 degrees is forbidden. Conversely in the a pi(-)pi(+) production the pions prefer to have a relative azimuthal angle 180 degrees and the production of the pions propagating together is suppressed. The dominant one-body mechanism in both channels is related to the excitation of the Delta isobar. Hence the reaction can serve as a source of information about Delta's properties in nucleus. We have found that the reaction is sensitive to effects of the pion and Delta renormalization in the nuclear medium, similar to those found in the coherent (gamma,pi(0)) reaction, but magnified because of the presence of the two pions. (C) 1997 Elsevier Science B.V. [References: 30]