The Impact of NLOCorrections on the Determination of the baru},bard} Content of Nucleon.pdfVIP

THE IMPACT OF NLO CORRECTIONS ON THE ¯ DETERMINATIONS OF THE u,¯ d CONTENT OF NUCLEONS FROM DRELL-YAN PRODUCTION 8 ¨ 9 W. SCHAFER 9 Institut f¨ur Kernphysik, Forschungszentrum J¨ulich, D-52425 J¨ulich 1 The interpretation of Drell-Yan production in terms of the antiquark densities n depends on NLO corrections. Besides the NLO corrections to the familiar annihi- u ∗ + − lation qq¯ → γ → l l , there is a substantial contribution from the QCD Compton J ∗ + − ∗ + − subprocesses gq → qγ → ql l and gq¯ → qγ → ql l . The beam and target 6 dependence of the two classes of corrections is different. We discuss the impact of ¯ this difference on the determination of the d − u¯ asymmetry in the proton from 1 the comparison of the pp and pn Drell-Yan production. v 6 ¯ 9 The substantial d −u¯ asymmetry of the nucleon sea is a striking manifesta- 2 tion of the leading twist nonperturbative mesonic effects in parton distributions 6 (for the recent review and references see 1). The first indirect experimental ev- 0 8 idence for this asymmetry has been deduced from t