Q^2 Dependence of the azimuthal Asymmetry in Unpolarized Drell-Yan

Abstract

We study the azimuthal asymmetry of the unpolarized Drell-Yan in the framework of the T-odd functions. We find, on the basis of quite general arguments, that for |{\bf q}_{\perp}| << Q such an asymmetry decreases as Q^{-2}, where {\bf q}_{\perp} and Q are respectively the transverse momentum and the center-of-mass energy of the muon pair. The experimental results support this conclusion.

Comments: 15 pages, 4 figures. Presented at "HiX2004", Marseille, July 26-28, 2004