Measurement of quarkonium production in proton--lead and proton--proton collisions at $5.02$ $\mathrm{TeV}$ with the ATLAS detector

TL;DR

This study measures how quarkonium production differs in proton-lead versus proton-proton collisions at 5.02 TeV, revealing suppression of certain states and no significant change for others, providing insights into nuclear effects on quarkonium production.

Contribution

It presents the first detailed measurement of quarkonium production modification in p+Pb collisions at 5.02 TeV with the ATLAS detector, including differential cross sections and nuclear modification factors.

Findings

No significant modification of J/ψ production in p+Pb.

Suppression of Υ(1S) at low transverse momentum in p+Pb.

Suppressed production of excited quarkonium states in p+Pb.

Abstract

The modification of the production of $J/\psi$, $\psi(\mathrm{2S})$, and $\mit{\Upsilon}(n\mathrm{S})$ ($n = 1, 2, 3$) in $p$+Pb collisions with respect to their production in $pp$ collisions has been studied. The $p$+Pb and $pp$ datasets used in this paper correspond to integrated luminosities of $28$ $\mathrm{nb}^{-1}$ and $25$ $\mathrm{pb}^{-1}$ respectively, collected in 2013 and 2015 by the ATLAS detector at the LHC, both at a centre-of-mass energy per nucleon pair of 5.02 TeV. The quarkonium states are reconstructed in the dimuon decay channel. The yields of $J/\psi$ and $\psi(\mathrm{2S})$ are separated into prompt and non-prompt sources. The measured quarkonium differential cross sections are presented as a function of rapidity and transverse momentum, as is the nuclear modification factor, $R_{p\mathrm{Pb}}$ for $J/\psi$ and $\mit{\Upsilon}(\mathrm{1S})$. No significant modification of the $J/\psi$ production is observed while $\mit{\Upsilon}(\mathrm{1S})$ production is found to be suppressed at low transverse momentum in $p$+Pb collisions relative to $pp$ collisions. The production of excited charmonium and bottomonium states is found to be suppressed relative to that of the ground states in central $p$+Pb collisions.