Resolving kinematic ambiguities in QCD predictions for Deeply Virtual Compton Scattering

TL;DR

This paper addresses ambiguities in QCD predictions for Deeply Virtual Compton Scattering caused by convention choices, showing how to minimize these ambiguities through specific reference frame selection.

Contribution

It demonstrates that selecting a particular reference frame reduces kinematic ambiguities in unpolarized DVCS observables, improving prediction accuracy.

Findings

Finite-$t$ and target mass corrections cancel ambiguities at $1/Q^2$ accuracy.

Choosing a frame aligned with photon momenta minimizes ambiguities.

The approach enhances the reliability of QCD predictions for DVCS.

Abstract

The existing QCD predictions for the Deeply Virtual Compton Scattering (DVCS) depend on the convention used for the skewedness parameter and on the reference frame used to define helicity amplitudes. These ambiquities are formally power-suppressed but numerically significant. They are cancelled by finite-$t$ and target mass corrections that have been calculated recently to the $1/Q^2$ accuracy. It turns out that these corrections can be minimized, at least for unpolarized observables, by choosing a specific reference frame where longitudinal directions are defined by the photon momenta.