Measurement of the gluon polarization \Delta G/G at COMPASS

TL;DR

The COMPASS experiment measured the gluon polarization in the nucleon using photon-gluon fusion events, finding a value consistent with zero within uncertainties, to understand the gluon's role in nucleon spin.

Contribution

This study provides the first measurement of gluon polarization G/G at COMPASS using high-p_t hadron pairs and charmed mesons, advancing the understanding of nucleon spin structure.

Findings

G/G = 0.06 1 0.31 (stat.) 1 0.06 (syst.)

Analysis of D0 and D0* events and high-p_t hadron pairs

Results suggest a small gluon polarization within uncertainties.

Abstract

One of the key objectives of the COMPASS experiment at CERN is the determination of the gluon contribution to the nucleon spin. The gluon polarization is measured via photon-gluon fusion in deep-inelastic scattering of 160 GeV/c polarized muons on a polarized 6LiD solid-state target. Photon-gluon fusion is tagged by the observation of charmed mesons or the production of hadron pairs with large transverse momenta p_t. The status of the analysis of the D0 and D0* events and of the high-p_t hadron pairs is shown. The gluon polarization \Delta G/G has been determined from the asymmetry of high-p_t hadron pairs with Q^2>1 GeV/c^2 in an analysis of the 2002/03 data as \Delta G/G=0.06 \pm 0.31 (stat.) \pm 0.06 (syst.).