Thermodynamically anomalous regions and possible new signals of mixed-phase formation

Abstract

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. 25.75.Nq Quark deconfinement, quark-gluon plasma production, and phase transitions 25.75.-q Relativistic heavy-ion collisions 25.75.Dw Particle and resonance production arXiv:1412.0718v2 [nucl-th]

Threshold Collision Energy of the QCD Phase Diagram Tricritical Endpoint

“…Moreover, at CFO the low energy signals are accompanied by the strong jumps of the pressure p and the effective number of degrees of freedom p/T 4 [6][7][8]. In contrast to these findings, the high energy signals are less pronounced and, hence, their interpretation is not straightforward [6,7,10] and, therefore, one needs additional analysis of the collision energy range √ s N N 7.6 − 9.2 GeV.…”

“…Thus, in addition to the thermodynamic and hydrodynamic signals of a possible phase transformation at the collision energy range √ s N N 7.6 − 9.2 GeV [6,7,10] the work [13], first of all, gives an additional and independent evidence in favor of such a transformation and, moreover, it provides us with the necessary statistical (fluctuation) signal. However, in combination with the previous findings on the signals of 1-st order phase transition at the collision energies √ s N N 4.3 − 4.9 GeV [6,7,10] one should conclude that these are the signals of two phase transitions and, therefore, at the vicinity of collision energies √ s N N 8.8 − 9.2 GeV there may exist not a CEP, but a 3CEP. It should be stressed that this is highly nontrivial conclusion, since neither the lattice QCD nor the QCD inspired field-theoretical models can presently tell us for sure whether QCD has the CEP or 3CEP.…”

“…Recently the thermodynamical and hydrodynamical signals of the mixed quark-gluonhadron phase formation were revealed [6,7] from the analysis of different irregularities observed at chemical freeze-out (CFO) [8][9][10]. Moreover, such signals were observed at two ranges of the center-of-mass collision energies, namely √ s N N 3.8 − 4.9 GeV and √ s N N 7.6 − 9.2 GeV [6,7,10]. The thermodynamic signals include two sharp peaks of the trace anomaly δ = ( −3p) T 4 (here , p and T denote, respectively, the energy density of the system, its pressure and temperature) observed at √ s N N = 4.9 GeV and √ s N N = 9.2…”

“…Thermodynamical and hydrodynamical signals in the low collision energy region can be easily interpreted since they can be related with each other via the generalized shock adiabat model [11,12] which shows that there is one-to-one correspondence between the peak of δ at CFO and the peak of δ at the shock adiabat [6,7]. Moreover, at CFO the low energy signals are accompanied by the strong jumps of the pressure p and the effective number of degrees of freedom p/T 4 [6][7][8]. In contrast to these findings, the high energy signals are less pronounced and, hence, their interpretation is not straightforward [6,7,10] and, therefore, one needs additional analysis of the collision energy range √ s N N 7.6 − 9.2 GeV.…”

Influence of the vector interaction and an external magnetic field on the isentropes near the chiral critical end point

“…[19], a sharp peak in the trace anomaly and a local minimum of the generalized specific volume at a laboratory energy of 11.6A GeV was observed which can provide a signal for the formation of a mixed phase between the quark-gluon plasma and the hadron phase. (iii) In Ref.…”