Study of $\Upsilon$ production in $p$Pb collisions at $\sqrt{s_{NN}}=8.16$ TeV

TL;DR

This paper reports measurements of $$Upsilon(nS)$$ meson production in proton-lead collisions at 8.16 TeV, analyzing cross-sections, ratios, and nuclear effects to understand quarkonium suppression.

Contribution

It provides the first detailed differential and integrated measurements of $$Upsilon(nS)$$ production in $p$Pb collisions at this energy, including comparisons to theoretical models.

Findings

Observation of quarkonium suppression in $p$Pb collisions.

Measurement of production ratios among $$Upsilon(1S), 2S, and 3S.

Differential cross-sections and nuclear modification factors are provided.

Abstract

The production of $\Upsilon(nS)$ mesons ($n=1,2,3$) in $p$Pb and Pb$p$ collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{NN}}=8.16$ TeV is measured by the LHCb experiment, using a data sample corresponding to an integrated luminosity of 31.8 nb$^{-1}$. The $\Upsilon(nS)$ mesons are reconstructed through their decays into two opposite-sign muons. The measurements comprise the differential production cross-sections of the $\Upsilon(1S)$ and $\Upsilon(2S)$ states, their forward-to-backward ratios and nuclear modification factors, performed as a function of the transverse momentum \pt and rapidity in the nucleon-nucleon centre-of-mass frame $y^*$ of the $\Upsilon(nS)$ states, in the kinematic range $p_{\rm{T}}<25$ GeV/$c$ and $1.5<y^*<4.0$ ($-5.0<y^*<-2.5$) for $p$Pb (Pb$p$) collisions. In addition, production cross-sections for $\Upsilon(3S)$ are measured integrated over phase space and the production ratios between all three $\Upsilon(nS)$ states are determined. The measurements are compared to theoretical predictions and suppressions for quarkonium in $p$Pb collisions are observed.