How well do we know the gluon polarization in the proton?

TL;DR

This paper presents a comprehensive global analysis of proton PDFs, focusing on the gluon polarization, revealing biases from common assumptions and enabling the first consistent extraction of helicity PDFs with uncertainty quantification.

Contribution

It introduces the first simultaneous global QCD analysis of spin-averaged and spin-dependent PDFs including jet data, critically assessing assumptions affecting gluon polarization.

Findings

Bias from SU(3) symmetry and positivity assumptions on gluon polarization

First extraction of helicity-aligned and antialigned PDFs with uncertainties

Impact of jet data on constraining gluon polarization

Abstract

We perform the first simultaneous global QCD analysis of spin-averaged and spin-dependent parton distribution functions (PDFs), including single jet production data from unpolarized and polarized hadron collisions. We critically assess the impact of SU(3) flavor symmetry and PDF positivity assumptions on the quark and gluon helicity PDFs, and find strong bias from these, particularly on the gluon polarization. The simultaneous analysis allows for the first time extraction of individual helicity-aligned and antialigned PDFs with a consistent treatment of uncertainties.