New results on quark helicity distributions and gluon polarization from the COMPASS experiment at CERN

Abstract

The new results on quark helicity distributions and on the gluon polarization ∆G/G from the COMPASS experiment will be presented. COMPASS is a DIS experiment using polarized muons with an energy of 160 GeV scattered off polarized deuteron and proton targets. Quark helicity distributions are obtained from inclusive and semi-inclusive reactions from the 2002-2004 and 2006 deuteron data and from the 2007 proton data. The gluon polarization ∆G/G is determined from photon-gluon fusion (PGF) events. Two methods based on LO QCD approximation are used to extract PGF events: the selection of open-charm events via the observation of D∗ and D0 mesons or of a pair of high-pT hadrons. The open-charm result is obtained from the 20022004 and 2006 data and it is updated with additional charm channels contributions. For these contributions a new method of the signal strength parameterization based on a neural network classification is used. The high-pT hadron pair result is obtained from the 2002-2004 data using a new method of accounting for background processes.