Next-to-leading order versus quark off-shellness and intrinsickTin the Drell-Yan process

We calculate the effects of next-to-leading order perturbative QCD as well as of the quark transverse motion and off-shellness on the Drell-Yan process cross section. By studying the s{yields}{infinity} behavior of the cross section in these approaches, we find that the effects of quark off-shellness and intrinsic-k{sub T} parametrize those of higher twists. In particular, the off-shellness of partons generates part of the K-factor type corrections to the leading order cross section. Higher-twist contributions to the p{sub T}-spectrum of the Drell-Yan pairs are found to be large for presently accessible energies. The evolution of quark off-shellness distribution with the hard scale is also studied.