Today, the scientists running the Compact Muon Solenoid detector at the Large Hadron Collider reported some of the first signs of unexpected physics happening at the LHC. After tracking the particles that have spilled out of some collisions, the CMS collaboration has detected a correlation among the angles at which many of them escape the collision. This sort of behavior has been seen before, but only in heavy ion collisions, and the initial report is cautious about trying to draw a specific connection between the two. But, if the results hold up, they may tell us something about the internal structure of the proton, and where most of its mass comes from.

Heavy ion collisions, like those produced in Brookhaven's Relativistic Heavy Ion Collider, cause the particles that normally inhabit the nucleus to break down. Instead of a collection of protons and neutrons, their internal components—quarks and gluons—exist in a fluid-like state that is termed a quark-gluon plasma. This plasma is short lived, but it lasts long enough for the particles that fly out of it engage in interactions that link the angles at which they exit the plasma.

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The protons used at the LHC have many fewer quarks and gluons among them, but the huge energies at which they collide causes the production of additional particles, as energy is converted into matter. The CMS group limited their analysis to what are called "high multiplicity" collisions, where over a hundred particles are produced in the collisions; presumably, this increases the chances that a high-density state occurs at the point of impact.

The CMS team observed the same sorts of correlations among the particles exiting the high multiplicity collisions. As they put it in their paper, the correlation "resembles similar features observed in heavy ion experiments." However, they're clearly not ready to say that this is a sign of a quark-gluon plasma; "The physical origin of our observation is not yet understood," they write. But the data from the LHC is continuing to ramp up, so there's a good chance that this lack of understanding will be temporary.

UPDATE: We talked briefly with Brookhaven's Raju Venugopalan, who gave us a different perspective on the results. Venugopalan suggested that the new results could tell us something about the internal structure of the proton and the quantum fluctuations that occur there. These fluctuations are responsible for much of the proton's mass, and therefore a substantial portion of the mass of normal matter.

Normally, these fluctuations occur far too quickly to be tracked. But, in an accelerator like the LHC, the particles are moving at nearly the speed of light; relativity tells us that time slows to a crawl at speeds approaching that of light, so the accelerator essentially freezes whatever is going on inside a proton in place. In this sense, it acts like a giant flash bulb, capturing a single instant in the proton's quantum fluctuations.

According to Venugopalan, a certain "ridge" seen in the data reflects the pre-collision structure of the gluons, the particles that bind quarks together inside a nucleus. During the collisions, the force provided by the gluons ultimately stretches and snaps, but its influence can be detected in the correlations among particles as they exit the collision. Since the gluons also account for the quantum effects that produce the proton's non-quark mass, the data can also provide some insight into this process, and hence where a lot of normal matter's mass comes from.

If we've already seen some of this at RHIC, why are the new results so interesting? "These results are complementary to similar observations at RHIC because they show for the first time that the ridge-like structure are fundamentally not a nuclear effect (they don't come from the geometry of overlapping protons in a nucleus)," said Venugopalan. "The nuclear collisions at RHIC may enhance the effect, but it is something intrinsic to the quantum fluctuations that make up the proton itself."

Listing image by CERN/CMS