Gluon polarisation in the nucleon and longitudinal double spin asymmetries from open charm muoproduction

The gluon polarisation in the nucleon has been determined by detecting charm production via D-0 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 correspond to an integrated luminosity of 2.8 fb(-1). The dominant underlying process of charm production is the photon-gluon fusion to a c (c) over 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) approximate to 13 (GeV/c)(2) and at an average gluon momentum fraction (x) approximate to 0.11. The longitudinal cross-section asymmetry for D-0 production is presented in bins of the transverse momentum and the energy of the D-0 meson. (C) 2009 Elsevier B.V. All rights reserved.