The spin structure functiong1pof the proton and a test of the Bjorken sum rule
Nuclear and High Energy Physics
Physics
QC1-999
FOS: Physical sciences
01 natural sciences
High Energy Physics - Experiment
Subatomär fysik
High Energy Physics - Phenomenology
High Energy Physics - Experiment (hep-ex)
High Energy Physics - Phenomenology (hep-ph)
Subatomic Physics
0103 physical sciences
DOI:
10.1016/j.physletb.2015.11.064
Publication Date:
2015-11-27T12:33:05Z
AUTHORS (208)
ABSTRACT
19 pages, 8 figures and tables<br/>New results for the double spin asymmetry $A_1^{\rm p}$ and the proton longitudinal spin structure function $g_1^{\rm p}$ are presented. They were obtained by the COMPASS collaboration using polarised 200 GeV muons scattered off a longitudinally polarised NH$_3$ target. The data were collected in 2011 and complement those recorded in 2007 at 160\,GeV, in particular at lower values of $x$. They improve the statistical precision of $g_1^{\rm p}(x)$ by about a factor of two in the region $x\lesssim 0.02$. A next-to-leading order QCD fit to the $g_1$ world data is performed. It leads to a new determination of the quark spin contribution to the nucleon spin, $����$ ranging from 0.26 to 0.36, and to a re-evaluation of the first moment of $g_1^{\rm p}$. The uncertainty of $����$ is mostly due to the large uncertainty in the present determinations of the gluon helicity distribution. A new evaluation of the Bjorken sum rule based on the COMPASS results for the non-singlet structure function $g_1^{\rm NS}(x,Q^2)$ yields as ratio of the axial and vector coupling constants $|g_{\rm A}/g_{\rm V}| = 1.22 \pm 0.05~({\rm stat.}) \pm 0.10~({\rm syst.})$, which validates the sum rule to an accuracy of about 9\%.<br/>
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