Color-glass condensate is a type of matter theorized to exist in atomic nuclei traveling near the speed of light. According to Einstein's theory of relativity, a high-energy nucleus appears length contracted, or compressed, along its direction of motion. As a result, the gluons inside the nucleus appear to a stationary observer 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, the color-glass condensate describes the walls themselves, and is an intrinsic property of the particles that can only be observed under high-energy conditions such as those at RHIC and possibly at the Large Hadron Collider as well.
"Color" in the name "color-glass condensate" refers to a type of charge that quarks and gluons carry as a result of the strong nuclear force. The word "glass" is borrowed from the term for silica and other materials that are disordered and act like solids on short time scales but liquids on long time scales. In the "gluon walls," the gluons themselves are disordered and do not change their positions rapidly because of time dilation. "Condensate" means that the gluons have a very high density.
The color-glass condensate is important because it is proposed as a universal form of matter that describes the properties of all high-energy, strongly interacting particles. It has simple properties that follow from first principles in the theory of strong interactions, quantum chromodynamics. It has the potential to explain many unsolved problems such as how particles are produced in high-energy collisions, and the distribution of matter itself inside of these particles.
Researchers at CERN believe they have created color-glass condensates during collisions of protons with lead ions. In these sorts of collisions, the standard outcome is that new particles are created and fly off in different directions. However, the Compact Muon Solenoid (CMS) team at the LHC found that in a sample of 2 million lead-proton collisions, some pairs of particles flew away from each other with their respective directions correlated. This correlation of directions is the anomaly that might be caused by the existence of a color-glass condensate while the particles are colliding.
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