Improved Measurement of the $\bar d / \bar u$ Asymmetry in the Nucleon Sea

TL;DR

This paper reports precise measurements of the anti-down to anti-up quark ratio in the proton sea over a wide range of Bjorken-$x$, confirming and extending previous findings and comparing with various models and experiments.

Contribution

It provides improved measurements of the $ar{d}/ar{u}$ asymmetry in the proton sea, extending the range to lower $x$ and comparing with multiple theoretical and experimental results.

Findings

Confirmed previous $ar{d}/ar{u}$ asymmetry measurements

Extended measurements to lower $x$ values

Compared results with various models and experiments

Abstract

Measurements of the ratio of Drell-Yan yields from an 800 \rm{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 anti-down ($\bar{d}$) to anti-up ($\bar{u}$) quark distributions in the proton sea is determined over a wide range in Bjorken-$x$. These results confirm previous measurements by E866 and extend them to lower $x$. From these data, $(\bar{d}-\bar{u})$ and $\int(\bar{d}-\bar{u})dx$ are evaluated for $0.015<x<0.35$. These results are compared with parameterizations of various parton distribution functions, models and experimental results from NA51, NMC, and HERMES.