Delta G from Compass

TL;DR

This paper reports measurements of gluon polarization in the nucleon using open charm and high-$p_T$ hadron pairs from the COMPASS experiment, providing new insights into the gluon's contribution to nucleon spin.

Contribution

It presents new experimental results on gluon polarization from the COMPASS experiment, utilizing open charm and high-$p_T$ hadron pair channels, with measurements at different $x_G$ and scales.

Findings

Gluon polarization from charm channel: $-0.57 \, ext{±} \, 0.41$ at $x_G \, ext{≈} \, 0.15$

Gluon polarization from high-$p_T$ hadron pairs: $0.016 \, ext{±} \, 0.058$ (stat.) and $\pm 0.055$ (syst.) at $x_G \, ext{≈} \, 0.085$

Results suggest a small or negative gluon polarization within the measured $x_G$ range.

Abstract

Measurements of the gluon polarization $\frac{\Delta G}{G}$ via the open charm channel and based on the helicity asymmetry of large transverse-momentum hadrons in the final state are presented. The data have been collected in the years 2002-2004 by the COMPASS experiment at CERN using a 160 GeV/c polarized muon beam scattered off a polarized $^6$LiD target. The new result for $\frac{\Delta G}{G}$ from the charm channel is $-0.57 \pm 0.41 (stat.)$ at $x_G \simeq 0.15$ and scale $\mu^2 \simeq 13 $ (GeV/c)$^2$. The gluon polarization from high-$p_T$ hadron pairs is $\frac{\Delta G}{G} = 0.016\pm 0.058 (stat.)\pm 0.055 (syst.)$ at $x_G \simeq 0.085^{+0.07}_{-0.035}$ ($Q^2 < 1$ (GeV/c)$^2$ and $\mu^2 \simeq 3$ (GeV/c)$^2$)