Collinear factorization of diphoton photoproduction at next to leading order

TL;DR

This paper calculates the NLO amplitude for near forward diphoton photoproduction within collinear factorization, demonstrating factorization validity and revealing new insights into GPDs across their domain.

Contribution

It provides the first NLO calculation for this process, showing factorization holds and expanding understanding of GPDs in diphoton production.

Findings

NLO amplitude includes both real and imaginary parts.

Factorization validated at NLO for this reaction.

Probes entire quark GPD domain.

Abstract

We calculate in the framework of collinear factorization the amplitude for the photoproduction of a near forward large mass diphoton at leading twist and next to leading order (NLO) in $\alpha_s$. We demonstrate the validity of factorization at this order, which was never achieved for such a reaction where the coefficient function describes a $2 \to 3$ hard process. While the Born order amplitude was purely imaginary and only probed the $x=\pm \xi$ cross-over line of generalized parton distributions (GPD) domain, the NLO result contains both a real and an imaginary part and probes the whole domain of definition of quark GPDs. The phenomenology of our results for medium (JLab) and higher energy (EIC) experiments will be developed in a future study.