Measurement of Upsilon Production for p+p and p+d Interactions at 800 GeV

TL;DR

This study measures Upsilon production in proton-proton and proton-deuterium collisions at 800 GeV, revealing that gluon distributions in protons and neutrons are very similar, with implications for understanding gluon content in nucleons.

Contribution

First high-statistics measurement of Upsilon production at 800 GeV on hydrogen and deuterium, showing gluon distributions in proton and neutron are nearly identical.

Findings

The cross section ratio σ(p+d→Upsilon)/2σ(p+p→Upsilon) is approximately unity.

Gluon-gluon fusion dominates Upsilon production at this energy.

Results contrast with Drell-Yan cross section ratios, indicating similar gluon distributions in proton and neutron.

Abstract

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, $\sigma (p + d \to \Upsilon) / 2\sigma (p + p\to \Upsilon)$, 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.