The interpretation of Drell-Yan production in terms of the antiquark densities depends on NLO corrections. Besides the NLO corrections to the familiar annihilation $q\bar{ q}\to \gamma^* \to l^+ l^-$, there is a substantial contribution from the QCD Compton subprocesses $gq \to q\gamma^* \to q l^+ l^-$ and $g\bar{ q} \to q\gamma^* \to q l^+ l^-$. The beam and target dependence of the two classes of corrections is different. We discuss the impact of this difference on the determination of the $\bar{ d}-\bar{ u}$ asymmetry in the proton from the comparison of the $pp$ and $pn$ Drell-Yan production.
Categories: hep-ph