A RELATIVISITIC DESCRIPTION OF THE QUASIFREE RADIATIVE PION-CAPTURE REACTION ON NUCLEI

摘要

We present a relativistic model for the reaction A(pi+, gammap)A - 1. This is an extension of our recent model for negative-pion photoproduction. The interaction of the pion with the target nucleon is comprised of the set of Born terms arising from the pseudovector from of the pion-nucleon interaction lagrangian, as well as s- and u-channel diagrams involving the propagation of the DELTA(1232). The bound and continuum nucleons are described by solutions of the Dirac equation with appropriate scalar and vector potentials, while the pion wave function is a solution of the Klein-Gordon equation containing a pion-nucleus optical potential. Calculations of the triple differential cross section d3sigma/dOMEGA(p)dOMEGA(gamma)dE(gamma) as well as the polarization of the final proton are presented for the kinematics of TRIUMF experiment 550. Under appropriate kinematic conditions the contribution of the DELTA(1232) is found to be dominant in this reaction. The results are sensitive to the choice of pion-nucleus optical potential but are not very sensitive to the nucleon interactions with the nucleus. We obtain qualitative agreement with data from TRIUMF experiment 550. [References: 16]