Production of $\varUpsilon(\textrm{nS})$ mesons in Pb+Pb and $pp$ collisions at 5.02 TeV

TL;DR

This paper measures the production of $ extrm{Upsilon}$ mesons in Pb+Pb and $pp$ collisions at 5.02 TeV, analyzing their suppression patterns to understand quark-gluon plasma effects.

Contribution

It provides the first detailed comparison of $ extrm{Upsilon}$ production in Pb+Pb and $pp$ collisions at this energy, including nuclear modification factors and suppression of excited states.

Findings

Significant suppression of excited $ extrm{Upsilon}$ states in Pb+Pb collisions.

Nuclear modification factors vary with centrality, $p_T$, and rapidity.

Results agree with theoretical models of quark-gluon plasma suppression.

Abstract

A measurement of the production of vector bottomonium states, $\varUpsilon(\textrm{1S})$, $\varUpsilon(\textrm{2S})$, and $\varUpsilon(\textrm{3S})$, in Pb+Pb and $pp$ collisions at a center-of-mass energy per nucleon pair of 5.02 TeV is presented. The data correspond to integrated luminosities of 1.38~$\textrm{nb}^{-1}$ of Pb+Pb data collected in 2018, 0.44 $\textrm{nb}^{-1}$ of Pb+Pb data collected in 2015, and 0.26 $\textrm{fb}^{-1}$ of $pp$ data collected in 2017 by the ATLAS detector at the Large Hadron Collider. The measurements are performed in the dimuon decay channel for transverse momentum $p_\textrm{T}^{\mu\mu} < 30$~ GeV, absolute rapidity $|y^{\mu\mu}|<1.5$, and Pb+Pb event centrality 0-80%. The production rates of the three bottomonium states in Pb+Pb collisions are compared with those in $pp$ collisions to extract the nuclear modification factors as functions of event centrality, $p_\textrm{T}^{\mu\mu}$, and $|y^{\mu\mu}|$. In addition, the suppression of the excited states relative to the ground state is studied. The results are compared with theoretical model calculations.