Gaining a deeper understanding of the nucleon structure remains one of the longstanding challenges of current hadron physics. This work presents an analysis of transverse-spin dependent azimuthal asymmetries in the Drell--Yan process, ^- + p^ ^* + X ^+ + ^- + X, based on data collected by the Common Muon and Proton Apparatus for Structure and Spectroscopy (COMPASS) Collaboration in 2015 and 2018. The data were obtained using a 190~GeV negative pion beam scattered off transversely polarised NH₃ target. The analysis introduces a new method of weighting asymmetries by powers of the dimuon pair transverse momentum relative to the beam. This technique provides direct access to certain k ₓ² moments of the transverse-momentum dependent parton distribution functions. These findings represent one of the most significant experimental advances in spin physics in recent years and are expected to remain a key reference point until new data from CLAS12, EIC, and LHCspin are available.
M. Niemiec (Fri,) studied this question.