Towards small-$x$ resummed parton distribution functions

TL;DR

This paper introduces small-$x$ resummation at NLLx accuracy into parton distribution functions, improving the fit to DIS data at small $x$ and enhancing gluon and singlet PDFs at high scales.

Contribution

It presents the first implementation of small-$x$ resummation at NLLx in the NNPDF framework, improving PDF fits at small $x$.

Findings

Resummation improves the fit to small-$x$ DIS data.

Gluon and singlet PDFs are enhanced at small-$x$ after resummation.

Resummation effects are more significant at small-$x$ and small-$Q^2$.

Abstract

We present preliminary results for fits of parton distribution functions (PDFs) which include the resummation of small-$x$ logarithms at NLLx accuracy, performed in the NNPDF framework. We observe an improvement in the description of DIS data at small values of Bjorken $x$ when resummation effects are included. The improvement is more marked when comparing NNLO+NLLx fits to NNLO ones, and is particularly noticeable for small-$x$ and small-$Q^2$ HERA inclusive structure functions. The main effect of the resummation is an enhancement of the gluon and singlet PDFs at small-$x$, which persists at high scales.