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

These proceedings summarize recent CMS measurements at the LHC that extract the squared speed of sound, cₛ², of strongly interacting matter at extreme temperatures from the multiplicity dependence of the mean transverse momentum in ultra-central lead-lead (PbPb) collisions at √sNN = 5.02\ TeV. The analysis yields cₛ² = 0.241 ± 0.002\, (stat) ± 0.016\, (syst) at an effective temperature of Teff = 219 ± 8\, (syst)\,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.