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$T$-Odd Effects in Unpolarized Drell-Yan Scattering

We consider the leading twist $T$-odd contributions as the dominant source of the $\cos 2ϕ$ azimuthal asymmetry in unpolarized $p\bar{p}\to μμ^+ X$ dilepton 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 $50 {\rm GeV}$ 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 {\em valence} quark effects.