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The spin structure function of the proton and a test of the Bjorken sum rule
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New results for the double spin asymmetry hmlsrc">he MathML source" class="mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S037026931500920X&_mathId=si2.gif&_user=111111111&_pii=S037026931500920X&_rdoc=1&_issn=03702693&md5=60e5ed137920277b1fa2d385b5893ba7">JSB inlineImage" height="18" width="18" alt="View the MathML source" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S037026931500920X-si2.gif">hContainer hidden">hCode">h altimg="si2.gif" overflow="scroll">A1hvariant="normal">ph> and the proton longitudinal spin structure function hmlsrc">he MathML source" class="mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S037026931500920X&_mathId=si1.gif&_user=111111111&_pii=S037026931500920X&_rdoc=1&_issn=03702693&md5=df4781a19460dc8a7b131b0c30a63a2c">height="18" width="16" alt="View the MathML source" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S037026931500920X-si1.gif">hContainer hidden">hCode">h altimg="si1.gif" overflow="scroll">g1hvariant="normal">ph> are presented. They were obtained by the COMPASS Collaboration using polarised 200 GeV muons scattered off a longitudinally polarised NH3 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 hmlsrc">he MathML source" class="mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S037026931500920X&_mathId=si3.gif&_user=111111111&_pii=S037026931500920X&_rdoc=1&_issn=03702693&md5=3971c9b5bde7cc446aaa4641b8338bd6">height="18" width="33" alt="View the MathML source" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S037026931500920X-si3.gif">hContainer hidden">hCode">h altimg="si3.gif" overflow="scroll">g1hvariant="normal">phy="false">(xhy="false">)h> by about a factor of two in the region hmlsrc">hImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S037026931500920X&_mathId=si4.gif&_user=111111111&_pii=S037026931500920X&_rdoc=1&_issn=03702693&md5=c90b74e4e071509a5ab0f1ac1e4d354d" title="Click to view the MathML source">x≲0.02hContainer hidden">hCode">h altimg="si4.gif" overflow="scroll">x0.02h>. A next-to-leading order QCD fit to the hmlsrc">hImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S037026931500920X&_mathId=si5.gif&_user=111111111&_pii=S037026931500920X&_rdoc=1&_issn=03702693&md5=2b2ba8da21658a2a4619de4ab36443fc" title="Click to view the MathML source">g1hContainer hidden">hCode">h altimg="si5.gif" overflow="scroll">g1h> world data is performed. It leads to a new determination of the quark spin contribution to the nucleon spin, ΔΣ, ranging from 0.26 to 0.36, and to a re-evaluation of the first moment of hmlsrc">he MathML source" class="mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S037026931500920X&_mathId=si1.gif&_user=111111111&_pii=S037026931500920X&_rdoc=1&_issn=03702693&md5=df4781a19460dc8a7b131b0c30a63a2c">height="18" width="16" alt="View the MathML source" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S037026931500920X-si1.gif">hContainer hidden">hCode">h altimg="si1.gif" overflow="scroll">g1hvariant="normal">ph>. The uncertainty of ΔΣ 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 hmlsrc">he MathML source" class="mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S037026931500920X&_mathId=si6.gif&_user=111111111&_pii=S037026931500920X&_rdoc=1&_issn=03702693&md5=7b016fddae32f570b7d2180bb5f97293">height="18" width="66" alt="View the MathML source" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S037026931500920X-si6.gif">hContainer hidden">hCode">h altimg="si6.gif" overflow="scroll">g1hvariant="normal">NShy="false">(x,Q2hy="false">)h> yields as ratio of the axial and vector coupling constants hmlsrc">hImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S037026931500920X&_mathId=si7.gif&_user=111111111&_pii=S037026931500920X&_rdoc=1&_issn=03702693&md5=796ceafc1cab98b3989adaeae63462bc" title="Click to view the MathML source">|gA/gV|=1.22±0.05 (stat.)±0.10 (syst.)hContainer hidden">hCode">h altimg="si7.gif" overflow="scroll">hy="false">|ghvariant="normal">Ahy="false">/ghvariant="normal">Vhy="false">|=1.22±0.05 hy="false">(stat.hy="false">)±0.10 hy="false">(syst.hy="false">)h>, which validates the sum rule to an accuracy of about 9%.

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