Extracting the speed of sound in quark-gluon plasma with ultrarelativistic lead-lead collisions at the LHC

(CMS collaboration) Hayrapetyan, Aram; ..., ...; Giljanović, Duje; Godinović, Nikola; Lelas, Damir; Šćulac, Ana; Kovač, Marko; Šćulac, Toni; Bargassa, Pedrame; Brigljević, Vuko; Chitroda, Bhakti Kanulal; Ferenček, Dinko; Mishra, Saswat; Starodumov, Andrey; Šuša, Tatjana; ..., ...; Zhokin, Alexander (2024) Extracting the speed of sound in quark-gluon plasma with ultrarelativistic lead-lead collisions at the LHC. Reports on progress in physics, 87 (7). ISSN 0034-4885

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Abstract

Ultrarelativistic nuclear collisions create a strongly interacting state of hot and dense quark-gluon matter that exhibits a remarkable collective flow behavior with minimal viscous dissipation. To gain deeper insights into its intrinsic nature and fundamental degrees of freedom, we determine the speed of sound in an extended volume of quark-gluon plasma using lead-lead (PbPb) collisions at a center-of-mass energy per nucleon pair of 5.02 TeV. The data were recorded by the CMS experiment at the CERN LHC and correspond to an integrated luminosity of 0.607 nb. The measurement is performed by studying the multiplicity dependence of the average transverse momentum of charged particles emitted in head-on PbPb collisions. Our findings reveal that the speed of sound in this matter is nearly half the speed of light, with a squared value of 0.241 0.002 (stat) 0.016 (syst) in natural units. The effective medium temperature, estimated using the mean transverse momentum, is 219 8 (syst) MeV. The measured squared speed of sound at this temperature aligns precisely with predictions from lattice quantum chromodynamic (QCD) calculations. This result provides a stringent constraint on the equation of state of the created medium and direct evidence for a deconfined QCD phase being attained in relativistic nuclear collisions.

Item Type:	Article
Uncontrolled Keywords:	High energy physics ; Experimental particle physics ; LHC ; CMS ; quark–gluon plasma ; speed of sound ; ultra-central ; QCD equation of state ; velocity: acoustic ; matter: interaction ; particle flow: collective phenomena ; photon: velocity ; multiplicity: dependence ; charged particle: transverse momentum ; nucleon: pair ; quark gluon: matter ; quantum chromodynamics ; CERN LHC Coll ; nucleus ; temperature ; flow ; collective ; viscosity ; deconfinement ; equation of state ; lattice ; CERN Lab
Subjects:	NATURAL SCIENCES > Physics
Divisions:	Division of Experimental Physics
Depositing User:	Lovorka Čaja
Date Deposited:	15 Oct 2024 12:20
URI:	http://fulir.irb.hr/id/eprint/9162
DOI:	10.1088/1361-6633/ad4b9b

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