QCD analysis of bar p N -> gamma* pi in the scaling limit

Abstract

We study the scaling regime of nucleon - anti-nucleon annihilation into a deeply virtual photon and a meson, bar p N -> gamma* pi. We obtain the leading twist amplitude in the kinematical region where it factorizes into an antiproton distribution amplitude, a short-distance matrix element related to nucleon form factor and the long-distance dominated transition distribution amplitudes which describe the nucleon to meson transition. We give the Q^2 evolution equation for these transition distribution amplitudes. The scaling of the cross section of this process may be tested at the proposed GSI intense anti-proton beam facility FAIR with the PANDA or PAX detectors. We comment on related processes such as pi N -> N' gamma* and gamma* N -> N' pi which may be experimentally studied at intense meson beams facilities and at JLab or Hermes, respectively.