Deviations from NLO QCD evolution in inclusive HERA data

TL;DR

This paper investigates potential deviations from NLO QCD evolution in HERA data, finding evidence consistent with small x resummation and nonlinear effects, but not with NNLO corrections.

Contribution

It introduces a method to compare structure function data with backward-evolved NLO fits, revealing deviations at small x.

Findings

Evidence for deviations consistent with small x resummation.

Deviations incompatible with NNLO corrections.

Results suggest nonlinear evolution effects may be relevant.

Abstract

We search for deviations from next-to-leading order QCD evolution in HERA structure function data. We compare to data predictions for structure functions in the small x region, obtained by evolving backwards to low Q^2 the results of a parton fit performed in the large Q^2 region, where fixed-order perturbative QCD is certainly reliable. We find evidence for deviations which are qualitatively consistent with the behaviour predicted by small x perturbative resummation, and possibly also by nonlinear evolution effects, but incompatible with next-to-next-to leading order corrections.