Angular Dependence of the Nuclear Enhancement of Drell-Yan Pairs

Abstract

We calculate the nuclear enhancement in the angular distribution of Drell-Yan pairs produced in proton-nucleus reactions. Nuclear effects are encoded in universal twist-4 parton correlation functions. We find that the Lam-Tung relation for the angular coefficients of the lepton-pair distribution holds for the double-hard, but not for the soft-hard contribution. We also predict that nuclear enhancement effects at RHIC energies can be large.

Comments: 4 pages LaTeX, 5 figures; v2: discussion in the summary extended, some references added; v3: manuscript somewhat shortened, eq. (9) added, accepted for publication in Phys. Rev. Lett