Extracting the speed of sound of QCD from transverse momentum fluctuations

Abstract

We extract the speed of sound ($c_s$) in the quark-gluon plasma from ATLAS data on the probability distribution of the transverse momentum per particle, $[p_T]$, in ultra-central Pb+Pb collisions. With an ideal detector, $c_s$ can be inferred from the rise of the mean $[p_T]$ with the collision multiplicity. In practice, however, low-$p_T$ particles escape detection, which biases the analysis. We show how to correct for this bias by using data on the variance of $[p_T]$, as well as information from the recently-measured $v_0(p_T)$. We also introduce a systematic method for deblurring the noise from the hadronization process. Assuming that the size of the quark-gluon plasma is independent of the hadron multiplicity in collisions at zero impact parameter, which is the scenario preferred both by high-energy QCD and heavy-ion data, we obtain $c_s/c=0.496\pm 0.008$ at temperature $T=221\pm 13$~MeV, in perfect agreement with first-principles calculations from lattice QCD.

Published version. 11 pages, 4 figures

References in corpus (21)

• The equation of state in (2+1)-flavor QCD
• Viscosity Information from Relativistic Nuclear Collisions: How Perfect is the Fluid Observed at RHIC?
• Alternative ansatz to wounded nucleon and binary collision scaling in high-energy nuclear collisions
• Multi-system Bayesian constraints on the transport coefficients of QCD matter
• Bayesian analysis of heavy ion collisions with the heavy ion computational framework Trajectum
• Relativistic hydrodynamics for heavy-ion collisions
• Transverse momentum fluctuations and their correlation with elliptic flow in nuclear collision
• Transverse-momentum fluctuations in relativistic heavy-ion collisions from event-by-event viscous hydrodynamics
• Correlations between flow and transverse momentum in Xe+Xe and Pb+Pb collisions at the LHC with the ATLAS detector: a probe of the heavy-ion initial state and nuclear deformation
• Effects of initial state fluctuations on the mean transverse momentum
• Disentangling sources of momentum fluctuations in Xe+Xe and Pb+Pb collisions with the ATLAS detector
• Non-Gaussian transverse momentum fluctuations from impact parameter fluctuations
• Accessing the speed of sound in relativistic ultracentral nucleus-nucleus collisions using the mean transverse momentum
• Track Reconstruction in a High-Density Environment with ALICE
• Evidence for the collective nature of radial flow in Pb+Pb collisions with the ATLAS detector
• Analytical insights into the interplay of momentum, multiplicity and the speed of sound in heavy-ion collisions
• Isospin diffusion from ${}^{40,48}$Ca${+}^{40,48}$Ca experimental data at Fermi energies: Direct comparisons with transport model calculations
• Impact parameter dependence of anisotropic flow: Bayesian reconstruction in ultracentral nucleus-nucleus 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
• Feasibility of measuring the speed of sound of the quark-gluon plasma from the multiplicity and mean $p_T$ of ultracentral heavy-ion collisions