In the naive Drell--Yan model, the angular distribution of the Drell--Yan process has zero $\cos2\phi$ modulation, where $\phi$ denotes the azimuthal angle of dimuons in the Collins--Soper frame. However, a sizable $\cos 2\phi$ dependence was observed in pion-induced Drell--Yan experiments, such as the NA10 and E615 experiments. The Boer--Mulders function is a transverse momentum dependent...
The $J/\psi$ particle is a spin-1 charmonium state with significant decay fraction towards lepton pairs. The distribution of decay particles from the $J/\psi$ is influenced by its spin alignment, which provides insights into different production mechanisms. SeaQuest, a fixed target experiment at Fermilab, was designed to observe muon pairs from charmonium and Drell-Yan production in $pp$ and...
Study of angular distributions in the Drell-Yan process is a valuable tool for unraveling the structure of hadrons. Measuring the $\cos2\phi$ angular dependence, where $\phi$ denotes the azimuthal angle of dimuons in the Collins-Soper frame, can be used to extract the Boer-Mulders (BM) function. The BM function describes the transverse-polarization asymmetry of quarks within an unpolarized...