A possible evidence of the hadron-quark-gluon mixed phase formation in nuclear collisions

The performed systematic meta-analysis of the quality of data description (QDD) of existing event generators of nucleus-nucleus collisions allows us to extract a very important physical information. Our meta-analysis is dealing with the results of 10 event generators which describe data measured in the range of center of mass collision energies from 3.1 GeV to 17.3 GeV. It considers the mean deviation squared per number of experimental points obtained by these event generators, i.e. the QDD, as the results of independent meta-measurements. These generators and their QDDs are divided in two groups. The first group includes the generators which account for the quark-gluon plasma formation during nuclear collisions (QGP models), while the second group includes the generators which do not assume the QGP formation in such collisions (hadron gas models). Comparing the QDD of more than a hundred of different data sets of strange hadrons by two groups of models, we found two regions of the equal quality description of data which are located at the center of mass collision energies 4.4-4.87 GeV and 10.8-12 GeV. At the collision energies below 4.4 GeV the hadron gas models describe data much better than the QGP one and, hence, we associate this region with hadron phase. At the collision energies between 5 GeV and 10.8 GeV and above 12 GeV we found that QGP models describe data essentially better than the hadron gas ones and, hence, these regions we associate with the quark-gluon phase. As a result, the collision energy regions 4.4-4.87 GeV and 10.8-12 GeV we interpret as the energies of the hadron-quark-gluon mixed phase formation. Based on these findings we argue that the most probable energy range of the QCD phase diagram (tri)critical endpoint is 12-14 GeV.

Thermodynamically Anomalous Regions and Possible New Signals of Mixed Phase Formation

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.

Thermodynamically Anomalous Regions As A Mixed Phase Signal

Using the most advanced model of the hadron resonance gas we reveal, at chemical freeze-out, remarkable irregularities such as an abrupt change of the effective number of degrees of freedom and 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. On the basis of the generalized shock adiabat model we show that these plateaus give evidence for the thermodynamic anomalous properties of the mixed phase at its boundary to the quark-gluon plasma (QGP). A new signal for QGP formation is suggested and justified.

Bimodality Phenomenon in Finite and Infinite Systems Within an Exactly Solvable Statistical Model

We present a few explicit counterexamples to the widely spread belief about an exclusive role of the bimodal nuclear fragment size distributions as the first order phase transition signal. In thermodynamic limit the bimodality may appear at the supercritical temperatures due to the negative values of the surface tension coefficient. Such a result is found within a novel exactly solvable formulation of the simplified statistical multifragmentation model based on the virial expansion for a system of the nuclear fragments of all sizes. The developed statistical model corresponds to the compressible nuclear liquid with the tricritical endpoint located at one third of the normal nuclear density. Its exact solution for finite volumes demonstrates the bimodal fragment size distribution right inside the finite volume analog of a gaseous phase. These counterexamples clearly demonstrate the pitfalls of Hill approach to phase transitions in finite systems.

A Scientific Analysis of the Preprint arXiv:1301.1828v1 [nucl-th]

Below we analyze the `critic statements made in the Preprint arXiv:1301.1828v1 [nucl-th]. The doubtful scientific argumentation of the authors of the Preprint arXiv:1301.1828v1 [nucl-th] is also discussed.