mgr Małgorzata Niemiec (University of Warsaw)

“Probing the Nucleon 3D Structure at the COMPASS Experiment”

Abstract:
Gaining a deeper understanding of the nucleon structure remains one of the longstanding challenges in hadron physics. This presentation explores the nucleon three-dimensional structure through Transverse Momentum Dependent (TMD) Parton Distribution Functions (PDFs). While semi-inclusive deep inelastic scattering has provided valuable insights into TMD PDFs, complementary processes, especially the Drell–Yan reaction, are crucial for a complete picture.
We focus on transverse-spin–dependent azimuthal asymmetries in the Drell–Yan process, π⁻ + p↑ → γ* + X → μ⁺ + μ⁻ + X, using data collected by the COMPASS Collaboration in 2015 and 2018 with a 190 GeV negative pion beam on a transversely polarised NH₃ target.
A key feature of the analysis is a novel weighting method, where asymmetries are weighted by powers of the dimuon transverse momentum.
This allows direct access to the first kₜ² moments of the Sivers and Boer–Mulders functions, providing new insights into the structure of the nucleon. These results serve as an important reference for future studies at the EIC and LHCspin.