Fitting DVCS at NLO and beyond

TL;DR

This paper develops a comprehensive theoretical framework for analyzing deeply virtual Compton scattering (DVCS) at next-to-leading and next-to-next-to-leading orders, enabling precise data fitting and testing of QCD factorization.

Contribution

It provides the first complete NLO and NNLO calculations of DVCS amplitudes within a conformal scheme, and introduces a new GPD parameterization for better perturbative convergence.

Findings

Formalism fits H1 and ZEUS DVCS data well.

Conformal symmetry simplifies higher-order calculations.

Regge-inspired Q^2 scaling law is inconsistent with small x_Bj data.

Abstract

We outline the twist-two analysis of deeply virtual Compton scattering (DVCS)within the conformal partial wave expansion of the amplitude, represented as a Mellin--Barnes integral. The complete next-to-leading order results, including evolution, are obtained in the MS and a conformal factorization scheme. Within the latter, exploiting conformal symmetry, the radiative corrections are evaluated up to next-to-next-to-leading order. Using a new proposed parameterization for GPDs, we study the convergence of perturbation theory and demonstrate for H1 and ZEUS measurements that our formalism is suitable for a fitting procedure of DVCS observables. We comment on a recent claim of a breakdown of collinear factorization and show that a Regge-inspired Q^2 scaling law is ruled out by small x_Bj DVCS data.