Gluon Polarisation in the Nucleon and Longitudinal Double Spin Asymmetries from Open Charm Muoproduction

TL;DR

This paper measures the gluon polarisation in the nucleon by analyzing charm production via D0 mesons in polarized muon-deuteron scattering, providing insights into the spin structure of the nucleon.

Contribution

It presents the first determination of gluon polarisation using open charm muoproduction data from the COMPASS experiment, employing a leading order QCD approach.

Findings

Average gluon polarisation (Delta g/g)_x = -0.49 ± 0.27 (stat) ± 0.11 (syst)

Gluon momentum fraction x ≈ 0.11 at scale mu^2 ≈ 13 GeV^2

Measured longitudinal asymmetries in D0 production across different kinematic bins

Abstract

The gluon polarisation in the nucleon has been determined by detecting charm production via D0 meson decay to charged K and pi in polarised muon scattering off a longitudinally polarised deuteron target. The data were taken by the COMPASS Collaboration at CERN between 2002 and 2006 and corresponds to an integrated luminosity of 2.8 fb^-1. The dominant underlying process of charm production is the photon-gluon fusion to a cc-bar pair. A leading order QCD approach gives an average gluon polarisation of (Delta g/g)_x= -0.49 +- 0.27(stat) +- 0.11(syst) at a scale mu^2 ~ 13 (GeV/c)^2 and at an average gluon momentum fraction (x) ~ 0.11. The longitudinal cross-section asymmetry for D0 production is presented in bins of the transverse momentum and the energy of the D0 meson.