Transverse single spin asymmetries in Drell-Yan processes

Recently, it has been shown, contrary to previous beliefs, that the kperpendicular distribution of quarks in a transversely polarized proton can be asymmetric. This 'Sivers effect' had already been used to explain transverse single spin asymmetry (SSA) observed in inclusive pion production p↑p→πX and p-bar↑p→πX. In such channels, however, other mechanisms, such as the 'Collins effect' (a kperpendicular asymmetric fragmentation of a transversely polarized quark into pions), may generate SSA. The Sivers asymmetry is used here to compute the SSA in Drell-Yan processes; in this case, by considering the differential cross section in the lepton-pair invariant mass, rapidity, and transverse momentum, other mechanisms that may originate SSA cannot contribute. Estimates for BNL RHIC experiments are given