Description and interpretation of DVCS measurements

TL;DR

This paper critiques the universality of GPD models in describing DVCS and DVMP data, introduces a new global fit for DVCS, and discusses the challenges in extracting Compton form factors from unpolarized proton measurements.

Contribution

It presents a new global DVCS fit that better matches experimental data and highlights the limitations of extracting CFFs from unpolarized measurements.

Findings

Universal GPDs fail to describe deep inelastic scattering data.

A new global DVCS fit aligns well with recent measurements.

CFFs are better interpreted through specific combinations rather than direct extraction.

Abstract

Having in mind the well-known limitations of certain models of generalized parton distributions (GPDs), we show that the allegedly universal GPDs, describing both deeply virtual Compton scattering (DVCS) and deeply virtual meson production (DVMP) data, fail to describe measurements of deep inelastic scattering. We present a new global DVCS fit that describes reasonably the world data set, which includes now also new measurements from Hall A and CLAS collaborations. We also explicitly illustrate that Compton form factors (CFFs) cannot be unambiguously extracted from photon electroproduction measurements off unpolarized proton alone and we argue that it is more reliable to interpret such measurements in terms of certain CFF combinations, where still some care is needed in order to estimate the propagated error.