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 6 LiD 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 Δg/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, ⟨Δg/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.