Thermodynamically Anomalous Regions and Possible New Signals of Mixed Phase Formation
K.A. Bugaev🇺🇦 · A.I. Ivanytskyi🇺🇦 · D.R. Oliinychenko🇺🇦 · V.V. Sagun🇺🇦 · I.N. Mishustin🇩🇪 · D.H. Rischke🇩🇪 · L.M. Satarov🇩🇪 · G.M. Zinovjev🇺🇦
Using an advanced version of the hadron resonance gas model we have found indications for irregularities in data for hadrons produced in relativistic heavy-ion collisions. These include an abrupt change of the effective number of degrees of freedom, a change of the slope of the ratio of lambda hyperons to protons at laboratory energies 8.6--11.6 AGeV, as well as highly correlated plateaus in the collision-energy dependence of the entropy per baryon, total pion number per baryon, and thermal pion number per baryon at laboratory energies 6.9-11.6 AGeV. Also, we observe a sharp peak in the dimensionless trace anomaly at a laboratory energy of 11.6 AGeV. On the basis of the generalized shock-adiabat model we demonstrate that these observations give evidence for the anomalous thermodynamic properties of the mixed phase at its boundary to the quark-gluon plasma. We argue that the trace-anomaly peak and the local minimum of the generalized specific volume observed at a laboratory energy of 11.6 AGeV provide a signal for the formation of a mixed phase between the quark-gluon plasma and the hadron phase. This naturally explains the change of slope in the energy dependence of the yield of lambda hyperons per proton at a laboratory energy of 8.6 GeV.