Transverse Spin Asymmetries in the Drell–Yan Process from COMPASS

The COMPASS Collaboration measured Transverse Spin Asymmetries in the Drell–Yan process. The measurement was done with a 190 GeV/c negative pion beam and a transversely polarized ammonia target. The data were taken during 2015 and 2018. The measured asymmetries, related to Transverse Momentum Dependent Parton Distribution Functions will be presented with a special focus on the Sivers asymmetry, which is related to the orbital angular momenta of the quarks inside the nucleon. The Sivers function was also accessed in COMPASS Semi-Inclusive Deep Inelastic Scattering measurement and is theoretically predicted to be of opposite sign compared to that in Drell–Yan. The results from the 2015 data analysis, which will be presented, favor the sign change scenario. The joint analysis of 2015 and 2018 Drell–Yan data will improve the experimental uncertainty.