Exclusive pion production in proton-nucleus collisions and the relativistic two nucleon dynamics

The exclusive pion production in a proton-nucleus collision, leading to two-body final states, is examined in a fully covariant two-nucleon model. We focus on the amplitudes which are dominated by the Δ(1232) resonance. Retaining the full covariant forms of the πNN and πN Δ vertices and employing a relativistic propagator for the delta isobar, expressions for various reaction amplitudes are derived. The bound state nucleon wave functions are obtained by solving the Dirac equation with appropriate scalar and vector potentials whereas the continuum wave functions are approximated by plane waves. The sensitivity of the calculated cross sections to the in-medium self-energy of the intermediate pion is investigated. It is found that the relative magnitudes of the so called target-emission and projectile-emission amplitudes depend strongly on the pion self-energy. A comparison with the available data for the 12C and 16O targets at the incident proton energy of 800 MeV supports our conclusions. ((orig.))