Leading-order determination of the gluon polarisation from semi-inclusive deep inelastic scattering data

Using a novel analysis technique the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality Q2>1(GeV/c)2., The data were obtained by the COMPASS experiment at CERN using a 160 GeV/c polarised muon beam impinging on a polarised 6LiD target., By analysing the full range in hadron transverse momentum pT the different pT-dependences of the underlying processes are separated using a neural-network approach., In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain the gluon polarisation Δ g/ g is evaluated at leading order in pQCD at a hard scale of μ2= ⟨ Q2⟩ = 3 (GeV / c) 2., It is determined in three intervals of the nucleon momentum fraction carried by gluons xg covering the range 0.04<xg<0.28 and does not exhibit a significant dependence on xg., The average over the three intervals ⟨ Δ g/ g⟩ = 0.113 ± 0., 038 (stat.)± 0., 036 (syst.) at ⟨ xg⟩ ≈ 0.10 suggests that the gluon polarisation is positive in the measured xg range.