Initial-state quark energy loss from Drell-Yan production in proton-proton and proton-nucleus collisions

Drell-Yan production cross sections were measured by the NA3 and E866 experiments, in p-Pt and pp collisions, as a function of the dimuon mass and x_F. We compare these measurements to next-to-leading order Drell-Yan calculations, made with the CT EQ6M parton densities modified (or not) by nuclear effects, using the EPS09 parameterization. The analysis of the data allows us to evaluate the initial-state quark energy loss. Drell-Yan measurements are ideally suited to isolate the initial-state parton energy loss, given the absence of final-state effects on the produced dimuon. Our study shows that these data indicate negligible quark energy loss and allow us to derive rather strict upper limits. For completeness, our study has been repeated using the less accurate measurements of Drell-Yan cross section ratios between heavy and light nuclear targets, provided by the E772 and E866 experiments. Our results provide an additional constraint on the models trying to explain quarkonium production in proton- nucleus collisions, as a function of quarkonium rapidity and collision energy, where initial- and final-state energy loss has frequently been assumed to play an important role, convoluted with several other complex mechanisms, including final-state quarko nium breakup, formation time effects, etc.