Difficulties in the description of Drell-Yan processes at low invariant mass and high transverse momentum

Abstract

We study the Drell-Yan cross section differential with respect to the transverse momentum of the produced lepton pair. We consider data with moderate invariant mass Q of the lepton pair, between 4.5 GeV and 13.5 GeV, and similar (although slightly smaller) values of the transverse momentum qT. We approach the problem by deriving predictions based on standard collinear factorization, which are expected to be valid toward the high-qT end of the spectrum and to which any description of the spectrum at lower qT based on transverse-momentum dependent parton distributions ultimately needs to be matched. We find that the collinear framework predicts cross sections that in most cases are significantly below available data at high qT. We discuss additional perturbative and possible non-perturbative effects that increase the predicted cross section, but not by a sufficient amount.