Volker Koch
Lawrence Berkeley National Laboratory
vkoch@lbl.gov

Gunther Roland
Massachusetts Institute of Technology
rolandg@mit.edu

Mikhail Stephanov
University of Illinois at Chicago
misha@uic.edu

Program Coordinator:
Laura Lee
lee@phys.washington.edu
(206) 685-3509

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The phase diagram of QCD is a subject of active theoretical and experimental research. The focus of this program is on properties of the phase diagram which can be studied by the upcoming heavy-ion collision experiments at RHIC/BNL, as well as SPS/CERN and FAIR/GSI. The QCD critical point, terminating a first-order phase transition line, is one of the most basic features that could be discovered in these experiments. Such a discovery would define the landscape of the QCD phase diagram.

Recent extensive Lattice QCD calculations have conclusively demonstrated that the temperature driven transition at zero baryon chemical potential is an analytic crossover. On the other hand, past and recent model calculations, as well as studies of the color-superconducting phase, strongly suggest a first order phase transition between the hadronic and quark-gluon plasma phases at large baryon chemical potential and lower temperature. Taken together, these two features would require existence of a critical point, at which, as the chemical potential is decreased and the temperature is increased, the first order transition line terminates and turns into a crossover. At the critical point the hadronic and the quark-gluon QCD phases, coexisting along the first-order line, fuse into one phase.

At the critical point the first order transition becomes continuous, resulting in long-range correlations and fluctuations at all length scales. Such peculiar properties of the equation of state open possibilities for distinct experimental signatures which can be used to discover the critical point. In a mathematical sense, the critical point is a true thermodynamic singularity of QCD. Its experimental discovery will put a permanent mark on the QCD phase diagram and anchor the location of the first order boundary.

The purpose of this program is to bring together theorists and experimentalists to assess possibilities to discover the QCD critical point in relativistic heavy ion collisions. Specifically, the program goals are to:

• Summarize the present status of Lattice QCD studies locating the QCD critical point. We envisage a forum in which the advantages and limitations of various approaches will be discussed by the experts with the aim to further develop existing methods as well as to conceive radically new approaches.

• Facilitate development of reliable models which are anchored in Lattice QCD, take maximum advantage of the first-principle knowledge of QCD dynamics, including perturbative QCD and low energy theorems, and/or based on recent theoretical developments, such as random matrices or holographic correspondence. A particular emphasis should be given to approaches which are suitable for modeling dynamical real-time processes necessary for the description of the heavy ion collisions.

• Make maximum use of the knowledge of the critical-point phenomena gained in other branches of physics, both theoretical and experimental, such as condensed matter physics and the nuclear liquid-gas phase transition studies.

• Develop and discuss experimental signatures for the critical point and for the first-order phase co-existence region. Up-to-date experimental results will be overviewed and the capabilities of current and future experimental facilities will be discussed. The program will provide an opportunity for a mutually enlightening exchange of knowledge and ideas between experimental and theoretical colleagues.