Impact of low-$x$ resummation on QCD analysis of HERA data

TL;DR

Incorporating $ ext{ln}(1/x)$-resummation into QCD fits to HERA data improves the description of the data and alters the low-$x$ gluon distribution, especially at low scales, addressing previous tensions in the analysis.

Contribution

This work introduces $ ext{ln}(1/x)$-resummation into HERAPDF fits, revealing its impact on data description and gluon PDFs at low $x$ and $Q^2$.

Findings

Resummation improves fit quality, especially for $F_L$

Gluon PDF becomes steeply rising at low $x$ and low $Q^2$

Resummation resolves tension in low-$x$, low-$Q^2$ region

Abstract

Fits to the final combined HERA deep-inelastic scattering cross-section data within the conventional DGLAP framework of QCD have shown some tension at low $x$ and low $Q^2$. A resolution of this tension incorporating $\ln(1/x)$-resummation terms into the HERAPDF fits is investigated using the xFitter program. The kinematic region where this resummation is important is delineated. Such high-energy resummation not only gives a better description of the data, particularly of the longitudinal structure function $F_L$, it also results in a gluon PDF which is steeply rising at low $x$ for low scales, $Q^2 \simeq 2.5$ GeV$^2$, contrary to the fixed-order NLO and NNLO gluon PDF.