Measurement of Upsilon Production for P+P and P+D Interactions at 800 GeV/C

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We report a high statistics measurement of Upsilon production with an 800 GeV/c proton beam on hydrogen and deuterium targets. The dominance of the gluon-gluon fusion process for Upsilon production at this energy implies that the cross section ratio, sigma(p + d -> Upsilon)/2 sigma(p + p -> Upsilon), is sensitive to the gluon content in the neutron relative to that in the proton. Over the kinematic region 0 < x(F) < 0.6, this ratio is found to be consistent with unity, in striking contrast to the behavior of the Drell-Yan cross section ratio sigma(p + d)(DY)/2 sigma(p + p)(DY). This result shows that the gluon distributions in the proton and neutron are very similar. The Upsilon production cross sections are also compared with the p + d and p + Cu cross sections from earlier measurements.