Angular Dependence of the Nuclear Enhancement of Drell-Yan Pairs

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 the Relativistic Heavy Ion Collider energies can be large.