The lepton angular distributions of the Drell-Yan process in fixed-target experiments are investigated by NLO and NNLO perturbative QCD. We present the calculated angular parameters λ, μ, ν and the degree of violation of the Lam-Tung relation, 1-λ-2ν, for the NA10, E615 and E866 experiments. Predictions for the ongoing COMPASS and SeaQuest experiments are also presented. The transverse momentum (qT) distributions of λ and ν show a clear dependence on the dimuon mass (Q) while those of μ have a strong rapidity (xF) dependence. Furthermore, λ and ν are found to scale with qT/Q. These salient features could be qualitatively understood by a geometric approach where the lepton angular distribution parameters are expressed in terms of the polar and azimuthal angles of the "natural axis" in the dilepton rest frame.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)