Gluon polarization in the nucleon from quasi-real photoproduction of high-pT hadron pairs

TL;DR

This paper measures the gluon polarization in the nucleon using quasi-real photoproduction of high-pT hadron pairs, finding it consistent with zero within uncertainties, thus providing insights into the nucleon's spin structure.

Contribution

It provides a new experimental determination of gluon polarization in the nucleon from quasi-real photoproduction data, using the COMPASS experiment at CERN.

Findings

Gluon polarization Delta G/G = 0.024 ± 0.089 (stat.) ± 0.057 (syst.)

Helicity asymmetry for selected events is close to zero

Results are at x_g = 0.095 and mu^2 ≈ 3 GeV^2

Abstract

We present a determination of the gluon polarization Delta G/G in the nucleon, based on the helicity asymmetry of quasi-real photoproduction events, Q^2<1(GeV/c)^2, with a pair of large transverse-momentum hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarized muon beam scattered on a polarized 6-LiD target. The helicity asymmetry for the selected events is <A_||/D> = 0.002 +- 0.019(stat.) +- 0.003(syst.). From this value, we obtain in a leading-order QCD analysis Delta G/G=0.024 +- 0.089(stat.) +- 0.057(syst.) at x_g = 0.095 and mu^2 =~ 3 (GeV}/c)^2.