LHC proton-lead collisions may have created new form of matter


November 28, 2012

A proton-lead nucleus collision (Image: CERN)

A proton-lead nucleus collision (Image: CERN)

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In September, the Large Hadron Collider (LHC) was being tuned to enable it to study proton-lead nucleus collisions for a data run next year. Eventually it ran and data was collected on the collisions for a period of four hours. When the data was analyzed, it revealed that some particle pairs produced in the collision were traveling in the same direction – a highly unusual situation. Although the data is not sufficient for certainty, the consensus appears to favor this as evidence for production of a color-glass condensate, a new form of exotic matter that has so far only existed as a theory.

The data analysis from the short proton-lead collision run at the LHC revealed an unexpected behavior. Normally (nearly universally), pairs of particles produced in the aftermath of collisions travel in opposite directions. However, in the LHC proton-lead collisions, particle pairs sometimes traveled in a common direction, far too many of them to be explained by conventional dynamics.

Making matters more mysterious was the observation that apparently unrelated particles located apart from one another in the detector also had a tendency to travel in a common direction, a result which MIT physics professor Gunther Roland called "somewhat unusual." The phenomenon has been dubbed the “ridge” because the parallel correlations produce a long, raised edge in certain types of data summary graphs.

Production of exotic phases of matter in high-energy collisions is perhaps best known in terms of the quark-gluon plasma. In normal matter, protons and neutrons are made of three quarks held together by gluons. When enough energy is supplied – such as when heavy nuclei such as gold or lead are collided – the protons and neutrons literally melt, producing the quark-gluon plasma.

Lead nuclei melting into a quark-gluon plasma as the result of a high-energy collision (Image: CERN)

This plasma has the properties of a nearly frictionless liquid which is so dense that it can sweep particles in front of it like a wave, which would cause some portion of the particle pairs to travel in the same direction, rather than in opposite directions. However, the LHC's proton-lead collisions did not have quite enough energy to form a quark-gluon plasma, so this is not likely to explain the results.

This leads us to the theoretical notion of a color-glass condensate. When particles travel at very high speeds, relativistic effects should cause them to accumulate large numbers of gluons that flatten out into a sheet upon which they are essentially fixed in position during the collision, as time dilation slows their motion. This theoretical gluon state is called a color-glass condensate. Gluons in a color-glass condensate would be strongly interacting, so it is likely that quantum entanglement may also have a role in explaining the unusual aspects of very-high-energy proton-lead collisions.

Several weeks of additional data on proton-lead collisions will be collected early in 2013. Analysis of the extra data may settle the matter of what is causing particle pairs to radiate so strangely. Whether the answer is formation of a color-glass condensate, or something even stranger, there is little question that the answer provide a major step in our understanding of exotic matter.

Source: LHC

Update: In response to a reader comment, this story was updated on Nov. 29, 2012, to replace references to "color-gluon" with "color-glass."

About the Author
Brian Dodson From an early age Brian wanted to become a scientist. He did, earning a Ph.D. in physics and embarking on an R&D career which has recently broken the 40th anniversary. What he didn't expect was that along the way he would become a patent agent, a rocket scientist, a gourmet cook, a biotech entrepreneur, an opera tenor and a science writer. All articles by Brian Dodson

Someone smack them over the nose with a rolled up news paper and tell them "NO... bad scientist".. LOL but seriously can they not do "STRANGE" things with matter until after 12/21/12. I have bet with a friend that the world will not end and this is one bet I do not want to lose.

Michael Mantion

color-gluon or color-glass, you are using 2 terms interchangeably and I think one is a mistake.

Rich Brumpton

Nonsense, we need to forge forward and delve into the creation and complete control of matter. The LHC is step one on that path. Smash away my brainy friends, smash away.

Chance Rose

I'm just a layman with a pretty poor knowledge of physics (chose chemistry and biology at school,IDIOT); but, thanks to watching and reading much of Lawrence Krauss's stuff, I have,at age 59, found a renewed interest in Astronomy/Cosmology/Physics etc., and find this news extremely exciting even if I don't have the mental ability to completely or even partially get my head round the possible ramifications of this discovery. I hope this amazing work is carried on unrestricted and hope I live to see and hear of many more fascinating discoveries...

Alan Reid

Thanks for all for the amazing article

Bro Amos Seo

What will be the end of this proton study? Another atomic bomb? I always worry about this. :'(

Mikha Wati
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