Determination of nuclear parton distribution functions and their uncertainties at next-to-leading order

TL;DR

This paper performs a global analysis of nuclear parton distribution functions (NPDFs) at next-to-leading order, estimating their uncertainties and discussing the limitations of current data in constraining gluon distributions.

Contribution

It provides a comprehensive NLO analysis of NPDFs, including uncertainty estimates and a code for calculating NPDFs at specific x and Q^2 values.

Findings

Valence-quark distributions are well determined.

Antiquark distributions are determined at x<0.1 but uncertain at x>0.2.

Gluon modifications remain poorly constrained due to data limitations.

Abstract

Nuclear parton distribution functions (NPDFs) are determined by global analyses of experimental data on structure-function ratios F_2^A/F_2^{A'} and Drell-Yan cross-section ratios \sigma_{DY}^A/\sigma_{DY}^{A'}. The analyses are done in the leading order (LO) and next-to-leading order (NLO) of running coupling constant \alpha_s. Uncertainties of the NPDFs are estimated in both LO and NLO for finding possible NLO improvement. Valence-quark distributions are well determined, and antiquark distributions are also determined at x<0.1. However, the antiquark distributions have large uncertainties at x>0.2. Gluon modifications cannot be fixed at this stage. Although the advantage of the NLO analysis, in comparison with the LO one, is generally the sensitivity to the gluon distributions, gluon uncertainties are almost the same in the LO and NLO. It is because current scaling-violation data are not accurate enough to determine precise nuclear gluon distributions. Modifications of the PDFs in the deuteron are also discussed by including data on the proton-deuteron ratio F_2^D/F_2^p in the analysis. A code is provided for calculating the NPDFs and their uncertainties at given x and Q^2 in the LO and NLO.