NLO collinear factorization of large mass diphoton photoproduction amplitude

We calculate large mass diphoton exclusive photoproduction in the framework of collinear QCD factorization at next to leading order in \alpha_sαs and at leading twist. Collinear divergences of the coefficient function are absorbed by the evolution of the generalized parton distributions (GPDs). This result enlarges the existing factorization proofs to 2 \to 32→3 processes, opening new reactions to a trustable extraction of GPDs.