Lepton angular distributions of Drell-Yan process in pQCD and a geometric approach

Abstract

The lepton angular distributions of the Drell-Yan process in the fixed-target experiments are investigated by NLO and NNLO perturbative QCD. We present the calculated angular parameters $\lambda$, $\mu$, $\nu$ and the degree of violation of the Lam-Tung relation, $1-\lambda -2\nu$, for the E615 experiment as well as predictions for the COMPASS experiment. Many salient features of transverse momentum and rapidity dependence could be qualitatively understood by a geometric approach.

5 pages, 2 figures; contribution to the proceedings of the XXVII. International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2019), April 8-12, 2019,Torino, Italy