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

Abstract

The gluon polarisation in the nucleon has been determined by detecting charm production via D0 meson decay to charged K and π 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 barc) pair. A leading order QCD approach gives an average gluon polarisation of <Δg/g>_x=−0.49±0.27(stat)±0.11(syst) at a scale μ^2≈13 (GeV/c)^2 and at an average gluon momentum fraction <x>≈0.11. The longitudinal cross-section asymmetry for D0 production is presented in bins of the transverse momentum and the energy of the D0 meson

Leading and next-to-leading order gluon polarization in the nucleon and longitudinal double spin asymmetries from open charm muoproduction

“…The results are based on a data sample collected between 2002 and 2007 and supersede the previously published ones [19] as they are based on an improved analysis method and on the full data sample; additional final state channels are added as well. Most of the data were collected with the deuteron target.…”

“…The method is similar to the one used in our previous publication [19]. The asymmetry A N can be used in various ways to evaluate the gluon polarisation hÁg=gi at LO or NLO QCD accuracy.…”

“…For the low purity sample D [19,33], this approach uses fits to the mass spectra which are sampled in bins of two variables, NN signal purity (from a parametrization without a LL in the training) and fP a LL . The former sorts the events according to their similar kinematic dependences, while the latter is used to ensure the anticorrelation between a LL and the signal purity.…”

“…In this paper, we present new results on hÁg=gi and the virtual photon-nucleon asymmetries obtained from charm production tagged by D meson decays in 160 GeV=c [19], since they are based on the full data sample and an improved analysis method; additional final state channels are added as well. The gluon polarization is determined assuming that open charm production is dominated by the PGF mechanism, Ã g !…”

Longitudinal and transverse spin asymmetries for inclusive jet production at mid-rapidity in polarizedp+pcollisions ats=200 GeVAdamczyk1, Agakishiev2, Aggarwal3 et al. 2012Phys. Rev. DSelf Cite805380View full textAdd to dashboardCite

“…Perturbative QCD analyses [18][19][20][21][22][23] of the Q 2 dependence of g 1 ðx; Q 2 Þ gave the first insights into possible gluon polarization contributions, but the precision is thus far limited by the Q 2 range that is accessible in the fixed-target experiments. Semi-inclusive DIS spin asymmetry measurements with identified pions and kaons have made it possible to delineate the quark and antiquark spin contributions by flavor, and measurements with hadron pairs and open charm mesons have shown sensitivity to gluon polarization [24][25][26][27][28].…”