“T-odd effects” in unpolarized Drell-Yan scattering

We consider the leading twist “T-odd” contributions as the dominant source of the cos2ϕ azimuthal asymmetry in unpolarized pp¯→μ−μ+X di-lepton production in Drell-Yan scattering. This asymmetry contains information on the distribution of quark transverse spin in an unpolarized proton. In a parton-spectator framework we estimate these asymmetries at 50 GeV center of mass energy. This azimuthal asymmetry is interesting in light of proposed experiments at GSI, where an anti-proton beam is ideal for studying the transversity properties of quarks due to the dominance of valence quark effects.