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

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arxiv 2401.06896 v3 pith:P33FZUAD submitted 2024-01-12 nucl-ex hep-ex

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

classification nucl-ex hep-ex
keywords collisionsspeedsoundquark-gluonlead-leadmattermediummomentum
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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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.

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Forward citations

Cited by 6 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Extracting the speed of sound of QCD from transverse momentum fluctuations

    hep-ph 2026-03 conditional novelty 7.0

    From ATLAS data on transverse-momentum fluctuations in ultra-central Pb+Pb collisions, the QGP speed of sound is extracted as 0.496 ± 0.008 at 221 ± 13 MeV, matching lattice QCD.

  2. Geometric Bias and Centrality Dependence of Jet Quenching in High-Energy Nuclear Collisions

    nucl-th 2026-04 unverdicted novelty 5.0

    A refined HIJING initial-condition model with geometric bias from impact-parameter effects, combined with Boltzmann jet transport, describes the centrality dependence of charged-hadron suppression in 5.02 TeV Pb+Pb co...

  3. Geometric Bias and Centrality Dependence of Jet Quenching in High-Energy Nuclear Collisions

    nucl-th 2026-04 conditional novelty 5.0

    Suppression of high-pT hadrons in peripheral Pb+Pb collisions is predominantly driven by initial-state geometric bias rather than final-state jet quenching.

  4. The size of the quark-gluon plasma in ultracentral collisions: impact of initial density fluctuations on the average transverse momentum

    nucl-th 2025-11 unverdicted novelty 5.0

    Volume variation with multiplicity in ultracentral collisions is small when total entropy scales with nuclear mass number, as shown by relating it to initial density fluctuation profiles.

  5. The shape of differential radial flow $v_0(p_T)$, not its zero-crossing, carries physical information

    nucl-th 2025-04 conditional novelty 5.0

    The shape of v0(pT), not its zero-crossing, encodes physical information about radial flow because centrality and normalization choices only shift the curve vertically without changing its form.

  6. A multi-differential constraint map for quarkonium suppression mechanisms in high-multiplicity pp and pPb collisions

    hep-ph 2026-06 unverdicted novelty 4.0

    Multi-differential constraint analysis of Υ(nS) suppression in high-multiplicity pp and pPb collisions favors an early, globally correlated, topology-sensitive mechanism over local-density or total-multiplicity control.