Did the LHC Catch a New Type of Matter: Color-Glass Condensate?

MIT physicists working at the LHC may have discovered a new kind of matter by accident. The existence of this type of matter, called “color-glass condensate,” was proposed shortly before the discovery.

The heavy-ion group, led by Gunther Roland, was colliding lead nuclei with protons at near the speed of light and measuring the explosion of subatomic particles flying out of the collision. They were only doing so as a way to establish what background noise would look like in their other experiments, so they could filter it out of their results.

But what they saw was a correlation in the direction the particles were flying out of the collision. After accounting for all the other variables, what should have been random appeared to have a pattern.

The experiment involved over 2 million collisions.

Why were the directions of the particles related to each other? Similar results have been seen in heavy ion collisions, where lead or gold nuclei are smashed together. Those collisions produce a wave of debris called quark-gluon plasma.

Quarks are the particles that make up protons, neutrons, and similar large particles. Gluons are the force-carrying particles that hold quarks together.

This debris is thought to sweep through the collision, dragging particles with it, and producing the observed relationships.

But quark-gluon plasma doesn’t explain these results, nor does it explain similar results observed about two years ago during proton-proton collisions.

Instead, the theory suggests, this effect could be caused by a wave of “color-glass condensate.”

First, why the name?

  • Color – This is the name of the “charge” carried by quarks and enforced by gluons. Like positive and negative charge in electric fields, “color” creates the attraction between quarks. But it is much more complicated, because there are 3 colors, unlike the 2 charges found in electric fields.
  • Glass – A glass behaves like a solid on short time scales and a liquid on long time scales. Color-glass condensate is theorized to exist when particles are traveling close to the speed of light. Relativity ensures that this causes time to slow down when it is measured by a “stationary” observer. This causes the material to behave in some ways more like a solid, since it is “frozen in time.”
  • Condensate – This refers to the fact that the material is very dense. At near light speed, otherwise spherical distributions are measured to be flattened into near circles with extreme density.

The theory is that, because color-glass condensate is “frozen in time,” its quantum behavior lasts longer. This transforms it into a medium which can carry quantum signals, allowing the particles within the collision to share information with each other.

The result is that particles “tell” each other which direction they are going, so that they can coordinate their movements.

In January, the team will revisit the phenomenon in the hopes of determining whether color-glass condensate is the cause of the phenomenon. They also hope to find out whether the phenomena in proton-proton, proton-lead, and lead-lead collisions are related.


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