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Measurement of Target Spin (in)dependent Asymmetries in Dimuon Production in Pion-Nucleon Collisions at COMPASS

Yu-Hsiang Lien, Alexandr Chumakov

SciPost Phys. Proc. 8, 028 (2022) · published 11 July 2022

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The exploration of the transverse spin structure of the nucleon is one of the main topics of the COMPASS phase-II experiment. In 2015 and 2018 COMPASS performed Drell–Yan (DY) measurements using a 190 GeV π− beam interacting with a transversely polarized NH3 target and unpolarized W target. The azimuthal asymmetries in DY with trans- versely polarized NH3 target are sensitive to various transverse momentum dependent parton distribution functions. Preliminary results on the Sivers asymmetry are consis- tent with the QCD prediction for a sign-change of Sivers functions in DY. The angular coefficients λ, μ and ν that describe the unpolarized part of the DY cross section have been extracted from the data collected with W target. The preliminary results on the angular coefficients indicate the violation of the Lam–Tung relation, consistent with the observation in earlier DY experiments with pion beams.

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