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Latest RHIC Results Make News Headlines at Quark Matter 2004

The Color Glass Condensate Debate

As postulated by some nuclear physics theorists, color glass condensate (CGC) may be another extreme, universal form of matter thought to be an intrinsic property of strongly interacting particles that can only be observed under high-energy conditions such as those at RHIC. If CGC exists, then it may explain many unsolved problems, such as how particles are produced in high-energy collisions and the distribution of matter itself inside of these particles. However, there is considerable controversy among nuclear physicists about the existence of CGC and the interpretation of RHIC data regarding its existence. The debate may not be settled until after RHIC is upgraded to become eRHIC.

According to Einstein’s theory of relativity, a high-energy particle appears to be Lorentz contracted, or compressed, along its direction of motion. As a result, the gluons inside one gold ion appear to the other ion as a “gluonic wall” traveling near the speed of light. At very high energies, the density of the gluons in this wall is seen to increase greatly. Unlike the quark-gluon plasma produced in the collision of such walls, CGC describes the walls themselves.

“Color” in the name color glass condensate refers to a type of charge that quarks and gluons carry as a result of the strong force. The word “glass” is borrowed from the term for silica and other disordered materials that act as solids over short time scales but as liquids over long time scales; in gluonic walls, the gluons themselves are disordered and do not change their positions rapidly because of Lorentz time dilation. “Condensate” means that the gluons have a very high density.

The Continuing Search for Quark-Gluon Plasma

“When we are convinced that we have found quark-gluon plasma, it will be a tremendous return in terms of knowledge on the nation’s investment in RHIC science, as well as very satisfying for the people involved,” concludes Thomas Kirk, Brookhaven’s Associate Laboratory Director for High Energy & Nuclear Physics. “Although we are optimistic about being able to report that discovery soon, we are exercising due caution about interpreting the results that RHIC has produced to date.” And so the search for quark-gluon plasma and other physics continues at RHIC.

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