Measurement of Upsilon production for p + p and p + d interactions at 800 GeV/c.

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