https://www.arxiv.org/pdf/nucl-ex/0501009

Experimental and theoretical challenges in the search for the quark-gluon plasma: The STAR Collaboration's critical assessment of the evidence from RHIC collisions

https://www.physi.uni-heidelberg.de/~fschney/2008SS-Preseminar/buballarev.pdf

NJL-model analysis of dense quark matter

New forms of QCD matter discovered at RHIC

The current status of theoretical studies on the quantum chromodynamics (QCD) phase diagram at finite temperature and baryon chemical potential is reviewed with special emphasis on the origin of various phases and their symmetry breaking patterns. Topics include quark deconfinement, chiral symmetry restoration, order of the phase transitions, QCD critical point(s), colour superconductivity, various inhomogeneous states and implications from QCD-like theories.

https://iopscience.iop.org/article/10.1088/0034-4885/74/1/014001/pdf

The phase diagram of dense QCD

Chiral effective model with the Polyakov loop

Several approaches to QCD with two {ital massless} quarks at finite temperature T and baryon chemical potential {mu} suggest the existence of a tricritical point on the boundary of the phase with spontaneously broken chiral symmetry. In QCD with {ital massive} quarks there is then a critical point at the end of a first order transition line. We discuss possible experimental signatures of this point, which provide information about its location and properties. We propose a combination of event-by-event observables, including suppressed fluctuations in T and {mu} and, simultaneously, enhanced fluctuations in the multiplicity of soft pions. {copyright} {ital 1998} {ital The American Physical Society }

Signatures of the Tricritical Point in QCD

The event-by-event fluctuations of suitably chosen observables in heavy ion collisions at CERN SPS, BNL RHIC, and CERN LHC can tell us about the thermodynamic properties of the hadronic system at freeze-out. By studying these fluctuations as a function of varying control parameters, it is possible to learn much about the phase diagram of QCD. As a timely example, we stress the methods by which present experiments at the CERN SPS can locate the second-order critical end point of the first-order transition between quark-gluon plasma and hadron matter. Those event-by-event signatures which are characteristic of freeze-out in the vicinity of the critical point will exhibit nonmonotonic dependence on control parameters. We focus on observables constructed from the multiplicity and transverse momenta of charged pions. We first consider how the event-by-event fluctuations of such observables are affected by Bose-Einstein correlations, by resonances which decay after freeze-out, and by fluctuations in the transverse flow velocity. We compare our thermodynamic predictions for such noncritical event-by-event fluctuations with NA49 data, finding broad agreement. We then focus on effects due to thermal contact between the observed pions and a heat bath with a given (possibly singular) specific heat, due to the direct coupling between themore » critical fluctuations of the sigma field and the observed pions. We also discuss the effect of the pions produced in the decay of sigma particles just above threshold after freeze-out on the inclusive pion spectrum and on multiplicity fluctuations. We estimate the size of these nonmonotonic effects, which appear near the critical point, including restrictions imposed by finite size and finite time, and conclude that they should be easily observable. (c) 1999 The American Physical Society.« less

http://www.if.pw.edu.pl/~kperl/EVO/9903292v2

Event-by-Event Fluctuations in Heavy Ion Collisions and the QCD Critical Point

We apply the Glasgow method for lattice QCD at finite chemical potential to a schematic random matrix model. In this method the zeros of the partition function are obtained by averaging the coefficients of its expansion in powers of the chemical potential. In this paper we investigate the phase structure by means of Glasgow averaging and demonstrate that the method converges to the correct analytically known result. We conclude that the statistics needed for complete convergence grows exponentially with the size of the system--in our case, the dimension of the Dirac matrix. The use of an unquenched ensemble at {mu}=0 does not give an improvement over a quenched ensemble. We elucidate the phenomenon of a faster convergence of certain zeros of the partition function. The imprecision affecting the coefficients of the polynomial in the chemical potential can be interpeted as the appearance of a spurious phase. This phase dominates in the regions where the exact partition function is exponentially small, introducing additional phase boundaries, and hiding part of the true ones. The zeros along the surviving parts of the true boundaries remain unaffected. (c) 2000 The American Physical Society.

M. A. Stephanov

Papers

Signatures of the Tricritical Point in QCD

Event-by-Event Fluctuations in Heavy Ion Collisions and the QCD Critical Point

Random matrices and the convergence of partition function zeros in finite density QCD