Leading order determination of the gluon polarisation from DIS events with high-pT hadron pairs

We present a determination of the gluon polarisation Δg / g in the nucleon, based on the longitudinal double-spin asymmetry of DIS events with Q² > 1 ^{(GeV / c) 2} including 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/c polarised muon beam scattering off a polarised ⁶LiD target. The gluon polarisation is evaluated by a Neural Network approach for three intervals of the gluon momentum fraction x_g covering the range 0.04 <x_g < 0.27. The values obtained at leading order in QCD do not show any significant dependence on x_g. Their average is Δg / g = 0.125 ± 0.060 (stat.) ± 0.063 (syst.) at average x_g = 0.09 and a scale of μ² = 3 ^{(GeV / c) 2}.