Abstract
The ATLAS heavy-ion program utilizes heavy-flavour hadrons to probe the hot, dense matter formed at the LHC. Quarkonium measurements have been performed in pp, p+Pb and Pb+Pb systems to study medium effects. The Pb+Pb results show a strong suppression of charmonium productions in more central events. Proton-lead interactions show little modification of the 1S charmonium state, but seem to indicate a centrality dependence of the 2S state. Upsilons have been studied in p+Pb and are found to show decreasing behaviour in more central collisions. Inclusive muons with pT above 4 GeV have been studied to provide insight on open-flavour production, and are found to be strongly suppressed in Pb+Pb collisions with a substantial and significant elliptic flow signal. Muon-hadron correlations have also been studied in the 2016 [see formula in PDF] = 8.16 TeV p+Pb data. There are clear indications of a near-side ridge, suggesting that similar mechanisms may be relevant for both the small and large systems.
Highlights
Measurements of quarkonium production and the azimuthal anisotropy of hadron production in p+Pb and Pb+Pb collisions provide opportunites to understand the cold nuclear matter (CNM) effects and the properties of hot and dense medium, quark gluon plasma (QGP), created in heavy-ion collisions
This paper presents a few measurements of this kind carried out using datasets collected by the ATLAS detector [1] from 2013 to 2016 in pp, p+Pb and Pb+Pb collisions at the LHC
Among CNM effects, modification of nPDFs, nuclear absorption, induced medium energy loss and gluon saturation can be quantified by the nuclear modification factor, the ratio of quarkonium production cross sections in A+A relative to the cross sections measured in pp collisions at the same centre-of-mass energy
Summary
Measurements of quarkonium production and the azimuthal anisotropy of hadron production in p+Pb and Pb+Pb collisions provide opportunites to understand the cold nuclear matter (CNM) effects and the properties of hot and dense medium, quark gluon plasma (QGP), created in heavy-ion collisions. Among CNM effects, modification of nPDFs, nuclear absorption, induced medium energy loss and gluon saturation can be quantified by the nuclear modification factor, the ratio of quarkonium production cross sections in A+A relative to the cross sections measured in pp collisions at the same centre-of-mass energy. The azimuthal anisotropy in particle dN/dφ distributions, usually described by a Fourier coefficient with nth order harmonic cos[n(φ − Ψn)] , vn, where φ is the azimuthal angle of the partical momentum, and Ψn is the experimental event plane angle of nth order. These measurements can provide valuable constraints on QGP transport property
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