Transverse momentum weighted Sivers asymmetries in SIDIS and Drell-Yan processes at COMPASS

Abstract

We investigate the transverse momentum weighted Sivers asymmetries in the processes with transversely polarized proton target, including the P hT zMp sin(φ h − φS) weighted asymmetry in charged hadron production in semi-inclusive deeply inelastic scattering (SIDIS) and the q T Mp sin(φS) weighted asymmetry in π − p Drell-Yan process. Due to the integration over the transverse momentum, the weighted asymmetries can be expressed as the product of the transverse-moments of the transverse momentum dependent (TMD) parton distribution functions (PDFs) and fragmentation functions (FFs). Using the parametrization for the Sivers function of the proton, the unpolarized PDFs of proton and pion, and the unpolarized FF of charged hadron, we present the numerical calculation for weighted Sivers asymmetries in SIDIS and Drell-Yan processes at the kinematics of COMPASS, and compare them with experimental data. We find that our prediction on the weighted Sivers asymmetry in SIDIS process is in agreement with the recent COMPASS measurement. Due to the relatively large uncertainties of the preliminary data from COMPASS Drell-Yan program, high precision experimental data are needed to test the sign change property of the Sivers function between SIDIS and Drell-Yan processes and to constrain the sea quark Sivers function.