Small- and large-x nucleon spin structure from a global QCD analysis of polarized Parton Distribution Functions

TL;DR

This paper analyzes the spin-dependent parton distribution functions of nucleons at small and large momentum fractions, comparing models with a global analysis to understand the nucleon spin structure and identify areas needing future experimental data.

Contribution

It provides a systematic comparison between theoretical models and the NNPDFpol1.1 global analysis, highlighting the potential for future experiments to refine our understanding of nucleon spin structure.

Findings

NNPDFpol1.1 effectively discriminates between different theoretical models.

Uncertainties remain large near x→0 and x→1 due to limited experimental data.

Future measurements at Electron-Ion Collider and Jefferson Lab can improve knowledge.

Abstract

I investigate the behavior of spin-dependent parton distribution functions in the regions of small and large momentum fractions $x$. I present a systematic comparison between predictions for relevant observables obtained with various models of nucleon spin structure and a recent global analysis of spin-dependent distributions, NNPDFpol1.1. Together with its unpolarized counterpart, NNPDF2.3, they form a mutually consistent set of parton distributions. Because they include most of the available experimental information, and are determined with a minimally biased methodology, these are especially suited for such a study. I show how NNPDFpol1.1 can discriminate between different theoretical models, even though NNPDF uncertainties remain large near the endpoints $x\to 0$ and $x\to 1$, due to the lack of experimental information. I discuss how our knowledge of nucleon spin structure may be improved at small-$x$ by future measurements at an Electron-Ion Collider, and at large-$x$ by recent measurements at Jefferson Lab, also in view of its $12$ GeV upgrade.