Leading and Next-to-Leading Order 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 using open charm production, applying neural networks to analyze data from the COMPASS experiment, and provides results at both leading and next-to-leading order QCD accuracy.

Contribution

It presents the first determination of the gluon polarisation at NLO accuracy using open charm muoproduction data.

Findings

Average gluon polarisation at LO: -0.06 +/- 0.21 (stat) +/- 0.08 (syst)

Average gluon polarisation at NLO: -0.13 +/- 0.15 (stat) +/- 0.15 (syst)

Analysis includes neural network techniques and multiple D^0 decay channels.

Abstract

The gluon polarisation in the nucleon was measured using open charm production by scattering 160 GeV/c polarised muons off longitudinally polarised protons or deuterons. The data were taken by the COMPASS collaboration between 2002 and 2007. A detailed account is given of the analysis method that includes the application of neural networks. Several decay channels of D^0 mesons are investigated. Longitudinal spin asymmetries of the D meson production cross-sections are extracted in bins of D^0 transverse momentum and energy. At leading order QCD accuracy the average gluon polarisation is determined as (Delta g/G)^LO=-0.06 +/- 0.21 (stat.) +/- 0.08 (syst.) at the scale <mu^2> ~13 (GeV/c)^2 and an average gluon momentum fraction <x>~ 0.11. For the first time, the average gluon polarisation is also obtained at next-to-leading order QCD accuracy as (Delta g/G)^NLO = -0.13 +/- 0.15 (stat.) +/- 0.15 (syst.) at the scale <mu^2> ~ 13 (\GeV/c)^2 and <x> ~ 0.20.