Overview of the COMPASS results on the nucleon spin

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• 作者：Celso Franco ^{celso@lip.pt" class="auth_mail" title="E-mail the corresponding author} ; on behalf of the COMPASS collaboration
• 关键词：Nucleon Spin ; Quark Helicity ; Gluon Helicity ; TMDs ; GPDs
• 刊名：Nuclear and Particle Physics Proceedings
• 出版年：2016
• 出版时间：April-June 2016
• 年：2016
• 卷：273-275
• 期：Complete
• 页码：2084-2090
• 全文大小：471 K

文摘

The COMPASS experiment [COMPASS, P. Abbon et al., The COMPASS experiment at CERN, Nucl. Inst. Meth. A577, 455 (2007)] at CERN is one of the leading experiments studying the nucleon spin. These studies are being carried on since 2002, by measuring hadrons produced in deep inelastic scattering (DIS) of 160 GeV/c and 200 GeV/c polarised muons off different polarised targets (NH₃ for polarised protons and ⁶LiD for polarised deuterons). One of the main goals is to determine how the total longitudinal spin projection of the nucleon, 1/2, is distributed among its constituents, quarks and gluons. We review here the recent results on the quark and gluon helicities obtained by COMPASS. The other major goal, whose fulfilment is needed for a complete understanding of the nucleon spin, is the determination of the transverse momentum dependent parton distributions (TMDs). Regarding this topic, the latest results on the Collins and Sivers asymmetries will be shown. The former is sensitive to the transverse spin structure of the nucleon, while the latter reflects the correlations between the quarks transverse momentum and the nucleon spin. This overview will conclude with a summary of the approved plans of COMPASS for the near future: the study of TMDs with a pioneering polarised Drell-Yan experiment and the measurement of generalised parton distributions (GPDs).