Accessing TMDs through the Cahn Effect*

We investigate the proton's intrinsic transverse-momentum distributions via the Cahn effect within the framework of transverse-momentum–dependent (TMD) factorization. The Cahn effect generates a characteristic azimuthal cosϕ modulation between the leptonic and hadronic planes in semi-inclusive deep inelastic scattering (SIDIS). In this talk, we analyze in detail the TMD parton distribution functions that contribute to this modulation and their nontrivial relations, which are constrained by the so-called equation-of-motion (EOM) relations. Our findings advance the ongoing program of TMD phenomenology and are directly relevant to SIDIS measurements at Jefferson Lab and the COMPASS experiment at CERN.