Abstract
Bottomonium, a bound state of a bottom quark and its antiquark, is an excellent probe of the hot and dense medium created in heavy-ion collisions. The ATLAS collaboration at the LHC collected two large datasets of pp and Pb + Pb collisions in 2017 and 2018 corresponding to integrated luminosities of 0.26 fb−1 and 1.38 nb−1 respectively, at a center-of-mass energy per nucleon pair of 5.02 TeV. Bottomonium states are reconstructed via the dimuon decay channel in the absolute rapidity range of |y| < 1.5, and their production in Pb + Pb collisions is compared to that in pp collisions to extract the nuclear modification factor, RAA, as a function of transverse momentum, absolute rapidity, and event centrality. In addition, the relative suppression of the excited states ϒ(nS) to the ground state ϒ(1S) is studied.
Highlights
In ultra-relativistic heavy-ion collisions, hadronic matter can experience a phase transition and turn into a state of deconfined quarks and gluons, Quark-Gluon Plasma (QGP)
Analysis prodecure In Pb + Pb collisions, the candidate events are collected with a trigger which requires one muon to pass the Level-1 Trigger (L1) and another muon candidate with pμT collisions, a more strict trigger is confirmed at the High-Level Trigger (HLT) with pμT > 4 GeV, and at least > 4 GeV to be found in the full Muon Spectrometer (MS) system
In addition to the results for Υ(1S) and Υ(2S), the combined results of excited states, Υ(2S+3S), are presented as Υ(3S) peaks are barely seen in Pb + Pb data
Summary
In ultra-relativistic heavy-ion collisions, hadronic matter can experience a phase transition and turn into a state of deconfined quarks and gluons, Quark-Gluon Plasma (QGP). In such collisions, heavy-flavor quarks, especially charm and bottom, are produced at a very early stage and can be used to characterize the properties of the QGP. A sequential suppression of quarkonium states depending on their binding energies has been proposed as a thermometer of the QGP. In addition to RAA, the double ratio of the excited-to-ground state production cross sections in Pb + Pb to pp collisions, ρΥA(AnS)/Υ(1S) = [σPΥb(n+PSb)/σPΥb(1+PSb)]/[σΥpp(nS)/σΥpp(1S)], is investigated to quantify binding-energy dependent suppression
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