Remarks on heavy-quark production in photon-nucleon and photon-photon collisions

Abstract

I discuss mechanisms of heavy quark production in (real) photon-nucleon and (real) photon - (real) photon collisions. In particular, I focuse on application of the Saturation Model. In addition to the main dipole-nucleon or dipole-dipole contribution included in recent analyses, I propose how to calculate within the same formalism the hadronic single-resolved contribution to heavy quark production. At high photon-photon energies this yields a sizeable correction of about 30-40 % for inclusive charm production and 15-20 % for bottom production. Adding all possible contributions to $e^+ e^- \to b \bar b X$ together removes a huge deficit observed in earlier works but does not solve the problem totally.