Alladi Ramakrishnan Hall

Transversity in SIDIS : From COMPASS to EIC

Athira Vijayakumar

University of Illinois, Urbana-Champaign

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) with transversely polarized nucleons, continues to be at the forefront of this investigation. Transverse-momentum dependent
(TMD) effects lead to an azimuthal asymmetry, where the final-state particles preferentially emerge to one side relative to the nucleon’s
transverse spin. This asymmetry provides crucial insights into the transverse motion of partons, enabling access to parton distribution and
fragmentation functions (PDFs and FFs). Among these, the transversity TMD PDF describes transversely polarized quarks in a transversely polarized
nucleon.

In 2022, COMPASS collected data with a 160 GeV muon beam on a transversely polarized deuteron target, providing new insights into the transversity
distribution of u and d quarks. I will discuss recent results from the 2022 data, their implications for the future EIC project, and how COMPASS
data, combined with the EIC’s extended phase space, will enhance our understanding of nucleon structure.