5th International Workshop On Critical Point and Onset of Deconfinement
By
Paul Sorensen, Brookhaven National Laboratory
On June 8th to the 12th, Brookhaven National Laboratory will host a workshop on the QCD Critical Point and the Onset of Deconfinement. One hundred participants will travel from around the world to attend the meetings. This is the 5th workshop in a series that started in 2004 with a workshop at the ECT* in Trento. Subsequent meetings were held at the University of Bergen in 2005, at the Galileo Galilei Institute in Florence in 2006 and the GSI/Darmstadt in 2007.
The purpose of the workshop series is to discuss theoretical and experimental progress in study of the phase diagram of nuclear matter. The predicted phase diagram contains several exotic and varied regions. One point on that diagram corresponds to the now familiar nucleus which was discovered in March 1911 by Ernst Rutherford. The nucleus was later found to be a bundle of protons and neutrons which in turn are bundles of three quarks bound together by gluons. Those quarks and gluons can become other forms of matter besides the nucleus which is represented by a point on the map of nuclear matter. At other temperatures and densities, we expect to find phases of matter such as a soup of unbound quarks and gluons (quark-gluon plasma), various arrangements of color super-conducting phases, and even a phase of matter that could involve quarks confined into nearly massless bundles. The borders between these regions are phase transitions. The transition from one region to another can be smooth or abrupt. Mapping out the locations of these transitions is one of the highest priorities for the nuclear physics community.
Figure 1 shows a schematic representation of the nuclear matter phase diagram taken from the cover of the Nuclear Science Advisory Committee's 2008 Long Range Plan. The figure shows various regions and the evolution of the matter created in heavy ion collisions as it expands and cools. Varying the center-of-mass energy of the heavy ion collision changes the baryon density so that an energy scan probes a large region of the diagram; making it possible to study the structure of the phase diagram.
Figure 1: A schematic representation of the phase diagram of nuclear matter which featured prominently on the cover of the latest NSAC Long Range Plan. A beam energy scan making use of the full capability of the RHIC facility will cover a region of the diagram where the critical point is likely located.
Experiments at RHIC have found evidence that when they collide nuclei together with very high energy, a strongly coupled quark-gluon plasma is created. The discovery of this phase was listed as the top physics story of 2005 by the American Institute of Physics and was widely covered in the popular press. Computer simulations carried out to solve the equations governing quarks and gluons (Lattice QCD) demonstrate that for the top RHIC energies used, the transition into and out of that phase is a smooth crossover. For lower energies, however, the transition is thought to be abrupt. The point where the transition changes from smooth to abrupt is an important landmark called the critical point. So far the Lattice QCD calculations have not been able to determine where the QCD critical point lies. Experiments therefore need to scan a large region of the phase diagram to locate the critical point. Detecting clear evidence that as it cools down, the matter in heavy-ion collisions passes through a first order phase transition or near the critical point is an experimental challenge which workshop participants will discuss extensively.
The workshop will feature 56 talks by experts in the field from 50 different institutions. The agenda for the meeting can be found on the workshop website: http://www.bnl.gov/cpod/
Local organizing committee
F. Karsch (Chair)
T. Ludlam
T. Satogata
P. Sorensen
G. Stephans
The Relativistic Heavy Ion Collider at Brookhaven National
Laboratory is a world-class scientific research facility primarily
funded by the U.S. Department of Energy Office of Science. Hundreds
of physicists from around the world use RHIC to study what the
universe may have looked like in the first few moments after its
creation. What physicists learn from these collisions may help us
understand more about why the physical world works the way it does,
from the smallest subatomic particles, to the largest stars.