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Extracting the speed of sound in quark–gluon plasma with ultrarelativistic lead–lead collisions at the LHC
File(s)
Author(s)
The CMS Collaboration
Type
Journal Article
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−1. 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.
Date Issued
2024-07-01
Date Acceptance
2024-05-14
Citation
Reports on Progress in Physics, 2024, 87 (7)
URI
URL
DOI
ISSN
0034-4885
Publisher
IOP Publishing
Journal / Book Title
Reports on Progress in Physics
Volume
87
Issue
7
Copyright Statement
© 2024 CERN, for the benefit of the CMS Collaboration. Original Content from this work may be used under the
terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and
the title of the work, journal citation and DOI.
License URL
Identifier
https://doi.org/10.1088/1361-6633/ad4b9b
Publication Status
Published
Article Number
ARTN 077801
Date Publish Online
2024-06-20