Mapping out the QCD phase transition in multiparticle production

We analyse multiparticle production in a thermal framework for seven central nucleus + nucleus collisions, e⁺ + e^- annihilation into hadrons on the Z resonance and four hadronic reactions (p + p and p + p̄ with partial centrality selection), with centre of mass energies ranging from √s = 2.6 GeV (per nucleon pair) to 1.8 TeV. Thermodynamic parameters at chemical freeze-out (temperature and baryon and strangeness fugacities) are obtained from appropriate fits, generally improving in quality for reactions subjected to centrality cuts. All systems with non-vanishing fugacities are extrapolated along trajectories of equal energy density, density and entropy density to zero fugacities. The so-obtained temperatures extrapolated to zero fugacities as a function of initial energy density ε_in universally show a strong rise followed by a saturating limit of T_lim = 155 ± 6 ± 20 MeV. We interpret this behaviour as mapping out the boundary between quark gluon plasma and hadronic phases. The ratio of strange antiquarks to light ones as a function of the initial energy density ε_in shows the same behaviour as the temperature, saturating at a value of 0.365 ± 0.033 ± 0.07. No distinctive feature of 'strangeness enhancement' is seen for heavy ion collisions relative to hadronic and leptonic reactions, when compared at the same initial energy density.