New Measurements of Transverse Spin Asymmetries at COMPASS

Over the past few decades, there has been enormous progress in understanding the internal structure of the nucleon, both on the experimental and theoretical sides. It has become clear that the proton’s spin budget cannot be fully explained by parton spin alone, suggesting a significant role for transverse motion and orbital angular momentum within the nucleon. The COMPASS experiment at CERN, using semi-inclusive deep inelastic scattering (SIDIS) and Drell-Yan production with transversely polarized nucleons, continues to be at the forefront of this investigation. Transverse-momentum and spin dependent effects lead to azimuthal asymmetries, where the final-state particles preferentially emerge to one side relative to the nucleon’s transverse spin. These asymmetries provide crucial insights into the transverse motion of partons, enabling access to transverse momentum dependent parton distribution and fragmentation functions. There has been scarcity of data, in particular, to access the 𝑑 quark distributions. To address this concern, in 2022, COMPASS collected SIDIS data with a 160 GeV muon beam on a transversely polarized deuteron target, providing new insights into the transversity and Sivers distributions of 𝑢 and 𝑑 quarks. After the analysis of part of 2022 data, the first results for Sivers and Collins asymmetries are discussed here. Additionally, dihadron asymmetries are also shown.