Longitudinal spin physics results from COMPASS

Abstract

The COMPASS experiment at the CERN SPS has a broad physics program focused on the nucleon spin structure and hadron spectroscopy, using muon and hadron beams, respectively. Results from the COMPASS on the inclusive longitudinal double spin asymmetries A1d,p measured in deep-inelastic polarized muon scattering off the polarized 6LiD and NH3 targets are presented. The new proton data cover the range Q2>1(GeV2/c), 0.004<x<0.7 and improve the statistical precision of g1p(x) by factor of two at x<0.02 compared to previous measurements. The spin-dependent non-singlet function g1NS(x,Q2) extracted from the data allows to evaluate the isovector quark density Δq3(x,Q2) and check the Bjorken sum rule prediction. The helicity distributions for the three lightest quark and antiquark flavours extracted from the measured double spin asymmetries for production of charged pions and kaons in semi-inclusive deep-inelastic scattering are also presented and discussed. The gluon polarization in the nucleon was determined using open charm production or high transverse-momentum hadron pairs production in polarized muon scattering off longitudinally polarized target.