The process p + pbar --> gamma + pi^0 within the handbag approch

Abstract

We analyse the exclusive channel $p\pb\to\gamma \pi^0$, assuming handbag dominance. The soft parts are parametrized in terms of CGLN amplitudes for the $q\qb\to\gamma \pi^0$ transition and form factors for the $p\pb\to q\qb$ ones, the latter represent moments of Generalized Distribution Amplitudes. We present a combined fit to Fermilab data from E760 taking simultaneously into account information from other exclusive reactions, especially from $p\pb\to \gamma\gamma$ data. Overall a nicely consistent picture emerges, such that one can hope, that our theoretical analysis will be reliable also for the kinematics of GSI/FAIR, which hopefully will provide much more precise and complete data. Consequently, data from this facility should improve our knowledge both on the proton-antiproton distribution amplitudes and the pion production mechanism.