Exchange process amplitudes in coherent pion production.

Abstract

Calculations have been done that assess the importance of projectile-generated and target-generated pions for the exclusive reaction [sup 12]C+[sup 12]C[r arrow][sup 12]C(15.11 MeV)+[sup 12]C+[pi][sup 0] below and near threshold. Both the amplitude for [Delta] formation in the target with subsequent decay to [pi][sup 0]'s while simultaneously exciting the projectile to the [ital M]1 giant resonant state at 15.11 MeV, and the exchange process amplitude, in which the target and projectile exchange roles, are included in the calculations for the pion triple differential cross sections. For the first time, results of the pion energy and pion angular and ejectile angular distributions are shown with both amplitudes properly included. Also for the first time in this work, pion and ejectile distributions are shown in the laboratory frame after the appropriate relativistic transformations are performed. The projectile-generated pion amplitude is the major contributor to the pion energy and ejectile angular distribution; whereas, both amplitudes are equally important in the pion angular distribution and give rise to a unique signature for coherent pion production as seen in the c.m. frame.