Parton momentum and helicity distributions in the nucleon

TL;DR

This paper reviews the current understanding of nucleon parton distribution functions, discussing formalism, data constraints, and future prospects for reducing uncertainties in spin-averaged and spin-dependent PDFs.

Contribution

It provides a comprehensive overview of the formalism, data constraints, and open questions in the global analysis of nucleon PDFs, including future experimental impacts.

Findings

Representative examples of unpolarized and polarized PDFs and their errors.

Discussion of constraints from various data types.

Anticipation of future experimental impacts on PDFs.

Abstract

We review the current status of spin-averaged and spin-dependent parton distribution functions (PDFs) of the nucleon. After presenting the formalism used to fit PDFs in modern global data analyses, we discuss constraints placed on the PDFs by specific data types. We give representative examples of unpolarized and polarized PDFs and their errors, and list open questions in global QCD fitting. Finally, we anticipate how future facilities, with fixed-target and collider experiments, may impact our knowledge of PDFs and reduce their uncertainties.