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

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 $\pm$ 0.002 (stat) $\pm$ 0.016 (syst) in natural units. The effective medium temperature, estimated using the mean transverse momentum, is 219 $\pm$ 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.

arXiv commentReplaced to correct one number in the previous version. All the figures and tables, including additional supplementary figures, can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/HIN-23-003 (CMS Public Pages)

References in corpus (28)

• Experimental and Theoretical Challenges in the Search for the Quark Gluon Plasma: The STAR Collaboration's Critical Assessment of the Evidence from RHIC Collisions
• Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration
• Quark Gluon Plasma an Color Glass Condensate at RHIC? The perspective from the BRAHMS experiment
• The PHOBOS Perspective on Discoveries at RHIC
• Collective flow and viscosity in relativistic heavy-ion collisions
• The equation of state in (2+1)-flavor QCD
• Particle-flow reconstruction and global event description with the CMS detector
• The QCD equation of state with dynamical quarks
• The CMS trigger system
• Description and performance of track and primary-vertex reconstruction with the CMS tracker
• Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at $\sqrt{s}=$ 13 TeV
• Performance of the CMS Level-1 trigger in proton-proton collisions at $\sqrt{s}=$ 13 TeV
• Electron and photon reconstruction and identification with the CMS experiment at the CERN LHC
• Centrality dependence of the charged-particle multiplicity density at mid-rapidity in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV
• Charged-particle nuclear modification factors in PbPb and pPb collisions at sqrt(s[NN]) = 5.02 TeV
• Constraining the Eq. of State of Super-Hadronic Matter from Heavy-Ion Collisions
• Heavy ion event generator HYDJET++ (HYDrodynamics plus JETs)
• Studies of azimuthal dihadron correlations in ultra-central PbPb collisions at sqrt(s[NN]) = 2.76 TeV
• Thermodynamics of hot strong-interaction matter from ultrarelativistic nuclear collisions
• Transverse momentum spectra and nuclear modification factors of charged particles in Xe-Xe collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.44 TeV
• Determination of the neutron skin of ${}^{208}$Pb from ultrarelativistic nuclear collisions
• Universal Sound Diffusion in a Strongly Interacting Fermi Gas
• Relating centrality to impact parameter in nucleus-nucleus collisions
• The mean transverse momentum of ultracentral heavy-ion collisions: A new probe of hydrodynamics
• Experimental equation of state in proton-proton and proton-antiproton collisions and phase transition to quark gluon plasma
• Mixed higher-order anisotropic flow and nonlinear response coefficients of charged particles in PbPb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 2.76 and 5.02 TeV
• Performance of the CMS Zero Degree Calorimeters in pPb collisions at the LHC
• Resonance Decay Contributions to Higher-Order Anisotropic Flow Coefficients

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• Feasibility of measuring the speed of sound of the quark-gluon plasma from the multiplicity and mean $p_T$ of ultracentral heavy-ion collisions
• Bayesian reconstruction of anisotropic flow fluctuations at fixed impact parameter
• The size of the quark-gluon plasma in ultracentral collisions: impact of initial density fluctuations on the average transverse momentum
• Rapidity dependence of mean transverse momentum fluctuation and decorrelation in baryon-dense medium
• High-order fluctuations of temperature in hot QCD matter
• Geometric Bias and Centrality Dependence of Jet Quenching in High-Energy Nuclear Collisions
• Blast-wave-Tsallis-power model for $p_{\mathrm{T}}$-spectra and elliptic flow $v_2$ of hadrons in collisions of identical nuclei at energies available at the Large Hadron Collider