Study of the thermodynamic properties of hot QCD matter with the CMS experiment

TL;DR

This paper reports CMS measurements of the squared speed of sound in hot QCD matter at the LHC, showing agreement with lattice-QCD predictions and exploring quark-gluon plasma signatures in different collision systems.

Contribution

It provides the first experimental extraction of the squared speed of sound in hot QCD matter at LHC energies, comparing results with theoretical models.

Findings

Measured $c_s^2$ as 0.241 with uncertainties in ultra-central PbPb collisions.

Found $c_s^2$ consistent with lattice-QCD calculations.

Explored quark-gluon plasma signatures in pPb collisions.

Abstract

These proceedings summarize recent CMS measurements at the LHC that extract the squared speed of sound, $c_s^2$, of strongly interacting matter at extreme temperatures from the multiplicity dependence of the mean transverse momentum in ultra-central lead-lead (PbPb) collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02\ \mathrm{TeV}$. The analysis yields $c_s^2 = 0.241 \pm 0.002\, (\mathrm{stat}) \pm 0.016\, (\mathrm{syst})$ at an effective temperature of $T_{\mathrm{eff}} = 219 \pm 8\, (\mathrm{syst})\,\mathrm{MeV}$, in good agreement with lattice-QCD calculations. Complementary studies in proton-lead (pPb) collisions are also presented to investigate possible quark-gluon plasma signatures in smaller systems.