Recent progress on nuclear parton distribution functions

TL;DR

This paper reviews recent advances in understanding nuclear parton distribution functions, highlighting current uncertainties, potential explanations for anomalies, and new insights into tensor-polarized distributions in spin-one hadrons.

Contribution

It provides an updated analysis of NPDFs, discusses nuclear clustering effects, and extracts tensor-polarized distributions, proposing future experimental directions.

Findings

Antiquark and gluon modifications have large uncertainties.

Nuclear modification differences may explain the NuTeV anomaly.

Tensor-polarized distributions can be tested in future experiments.

Abstract

We report current status of global analyses on nuclear parton distribution functions (NPDFs). The optimum NPDFs are determined by analyzing high-energy nuclear reaction data. Due to limited experimental measurements, antiquark modifications have large uncertainties at x>0.2 and gluon modifications cannot be determined. A nuclear modification difference between u and d quark distributions could be an origin of the long-standing NuTeV sin^2 theta_w anomaly. There is also an issue of nuclear modification differences between the structure functions of charged-lepton and neutrino reactions. Next, nuclear clustering effects are discussed in structure functions F_2^A as a possible explanation for an anomalous result in the Be-9 nucleus at the Thomas Jefferson National Accelerator Facility (JLab). Last, tensor-polarized quark and antiquark distribution functions are extracted from HERMES data on the polarized structure function b_1 of the deuteron, and they could be used for testing theoretical models and for proposing future experiments, for example, the one at JLab. Such measurements could open a new field of spin physics in spin-one hadrons.