'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-bar→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