New results from Fermilab E866 (NuSea) for

The Fermilab dimuon experiment 866/NuSea measured Drell-Yan yields from an 800 GeV/c proton beam incident on liquid hydrogen and deuterium targets. Over 370,000 Drell-Yan muon pairs were recorded. From these data, the ratio of anti-down (d) to anti-up (u) quark distributions in the proton sea is determined over a wide range in Bjorken-x. A strong x dependence is observed in the ratio du, showing substantial enhancement of d with respect to u for x < 0.2. The results presented here for the full data sets confirm previously published results from E866 and are compared with parametrizations of parton distribution functions calculated both before and after the publication of the high-mass E866 data.