Improved measurement of thed¯/ūasymmetry in the nucleon sea

Measurements of the ratio of Drell-Yan yields from an $800\hspace{0.5em}\mathrm{GeV}/c$ proton beam incident on liquid hydrogen and deuterium targets are reported. Approximately 360 000 Drell-Yan muon pairs remained after all cuts on the data. From these data, the ratio of down antiquark $\left(\overline{d}\right)$ to up $\left(ū\right)$ antiquark distributions in the proton sea is determined over a wide range in Bjorken-$x.\mathrm{}$ These results confirm previous measurements by E866 and extend them to lower x. From these data, $\left(\overline{d}-ū\right)$ and $\int \left(\overline{d}-ū\right)dx$ are evaluated for $0.015<x<\mathrm{}\mathrm{0.35.}\mathrm{}$ These results are compared with parametrizations of various parton distribution functions, models and experimental results from NA51, NMC and HERMES.