New Signals of Quark-Gluon-Hadron Mixed Phase Formation

TL;DR

This paper identifies irregularities at chemical freeze-out in heavy-ion collisions, including a trace anomaly peak and quasi-plateaus, providing evidence for a quark-gluon-hadron mixed phase and potential phase transitions.

Contribution

It introduces new signals and observables indicating the formation of a mixed phase and possible phase transitions in high-energy nuclear collisions.

Findings

Sharp trace anomaly peak at 4.9 GeV freeze-out energy

Two sets of correlated quasi-plateaus at specific energies

Evidence for anomalous thermodynamic properties in the mixed phase

Abstract

Here we present several remarkable irregularities at chemical freeze-out which are found using an advanced version of the hadron resonance gas model. The most prominent of them are the sharp peak of the trace anomaly existing at chemical freeze-out at the center of mass energy 4.9 GeV and two sets of highly correlated quasi-plateaus in the collision energy dependence of the entropy per baryon, total pion number per baryon, and thermal pion number per baryon which we found at the center of mass energies 3.8-4.9 GeV and 7.6-10 GeV. The low energy set of quasi-plateaus was predicted a long time ago. On the basis of the generalized shock-adiabat model we demonstrate that the low energy correlated quasi-plateaus give evidence for the anomalous thermodynamic properties inside the quark-gluon-hadron mixed phase. It is also shown that the trace anomaly sharp peak at chemical freeze-out corresponds to the trace anomaly peak at the boundary between the mixed phase and quark gluon plasma. We argue that the high energy correlated quasi-plateaus may correspond to a second phase transition and discuss its possible origin and location. Besides we suggest two new observables which may serve as clear signals of these phase transformations.