Constraining the polarized gluon PDF in pp collisions at RHIC

TL;DR

This paper discusses how measurements at RHIC using polarized proton collisions help determine the polarization of gluons inside protons, contributing to understanding the proton spin structure.

Contribution

It presents new constraints on the polarized gluon PDF Delta-g(x) derived from RHIC collision data.

Findings

Constraints on gluon polarization at various x values

Improved understanding of gluon contribution to proton spin

Data supports specific models of gluon polarization

Abstract

The main focus of the physics program at PHENIX and STAR that makes use of RHIC's polarized proton beams is to figure out how and if at all the gluons inside protons are polarized, or to put it another way, do the spin 1 gluons prefer to have their spins aligned or anti-aligned with the spin of the proton, or do they just not care? This question is an important part of the more general question of how the constituents of protons, gluons and quarks, conspire to make up the overall spin 1/2 of the proton. Measurements of, e.g, jet and hadron, production cross-section differences between the two cases where the two polarized protons colliding have their spins aligned and anti-aligned are sensitive to the gluon polarization, which is encoded in the spin--dependent parton distribution function (PDF) for gluons, Delta-g(x).