Measurement of the Upsilon Production Cross Section in 920 GeV Fixed-Target Proton-Nucleus Collisions

TL;DR

This paper reports the measurement of the Upsilon production cross section in 920 GeV fixed-target proton-nucleus collisions, providing new data on bottomonium production at this energy.

Contribution

First measurement of Upsilon production cross section in fixed-target proton-nucleus collisions at 920 GeV.

Findings

Upsilon to dilepton decay ratio R = (9.0 ± 2.1) x 10^-6

Upsilon production cross section at mid-rapidity = 4.5 ± 1.1 pb/nucleon

Results contribute to understanding bottomonium production mechanisms

Abstract

The proton-nucleon cross section ratio $R=Br(\Upsilon\to l^+l^-) d\sigma(\Upsilon)/dy|_{y=0} / {\sigma(J/\psi)}$ has been measured with the HERA-B spectrometer in fixed-target proton-nucleus collisions at 920 GeV proton beam energy corresponding to a proton-nucleon cms energy of sqrt{s}=41.6 GeV. The combined results for the Upsilon decay channels Upsilon $\to e^+e^-$ and Upsilon $\to\mu^+\mu^-$ yield a ratio $R=(9.0 \pm 2.1) 10^{-6}$. The corresponding Upsilon production cross section per nucleon at mid-rapidity (y=0) has been determined to be $Br(\Upsilon\to{}l^+l^-) {d\sigma(\Upsilon)/dy}|_{y=0}= 4.5 \pm 1.1 $ pb/nucleon.