Exclusive quasifree pion photoproduction on complex nuclei in the Delta region.

Abstract

We present an analysis of the reaction A(\ensuremath{\gamma},\ensuremath{\pi}N)B in the full distorted wave impulse approximation carried out in momentum space. The bound nucleon is in a single particle orbital while the outgoing pion and nucleon are described by appropriate optical potential wave functions. The pion photoproduction operator of Blomqvist and Laget is used. This reaction allows for more direct studies of \ensuremath{\Delta} properties in the nuclear medium than the reaction A(\ensuremath{\gamma},\ensuremath{\pi})B since the final nucleon is no longer bound and the sensitivity to the nuclear structure of the target is thereby largely reduced. Kinematically, the reaction provides a great deal of flexibility because the target can take up a wide range of momentum transfer and little energy. Our calculations agree roughly with data from Tomsk but overestimate data from Bates. Nonlocal effects tend to enhance the total cross sections and in some cases are significant. For future experiments we propose kinematics that greatly reduce uncertainties from the optical potentials and expose information from the production vertex. We find that photon asymmetry contains such information in the cleanest way and it should be pursued. We suggest forward pion angles where discrepancies between data and theory exist should be studied more carefully by experiments.