EPJ Web of Conferences 80, 00025 (2014)
https://doi.org/10.1051/epjconf/20148000025

Recent COMPASS results on the nucleon longitudinal spin structure and QCD fits

CEA Saclay, IRFU/SPhN, 91191 Gif-sur-Yvette, France

^a e-mail: vincent.andrieux@cern.ch
^b e-mail: fabienne.kunne@cern.ch, andrea.bressan@cern.ch

Published online: 24 November 2014

Abstract

The latest measurements of the proton longitudinal spin structure function, ɡ₁^p, in the deep inelastic (DIS) regime are presented. They improve the statistical accuracy of the existing data and extend the kinematic domain to a lower value of x and higher values of Q². A global NLO QCD fit of all ɡ₁ world data on the proton, deuteron and neutron has been achieved. The results give a quantification of the quark spin contribution to the nucleon spin, 0.26 < ΔΣ < 0.34 at 3 (GeV/c)² in M̅S̅ scheme. The errors are dominated by the uncertainty on the shape of the functional forms assumed in the fit. A new verification of the fundamental Bjorken sum rule is obtained at a 9% level, using only COMPASS ɡ₁ proton and deuteron measurements. Preliminary results of a reevaluation of the gluon polarization Δɡ/ɡ are presented. The analysis is based on double spin asymmetry of high-p_T hadron production cross-sections in the DIS regime. A positive value of 〈Δɡ/ɡ〉 = 0.113 ± 0.038 ± 0.035 is obtained at leading order at x ~ 0.1. In parallel, the double spin asymmetry in the photoproduction regime is also studied. Finally, preliminary results on quark fragmentation functions into pions extracted from a LO fit of pion multiplicities in semi-inclusive DIS are presented.