See Inside February 2011

Particles That Flock: Strange Synchronization Behavior at the Large Hadron Collider

Scientists at the Large Hadron Collider are trying to solve a puzzle of their own making: why particles sometimes fly in sync

Copyright CERn, for the benefit of the CMS Collaboration

In its first six months of operation, the Large Hadron Collider near Geneva has yet to find the Higgs boson, solve the mystery of dark matter or discover hidden dimensions of spacetime. It has, however, uncovered a tantalizing puzzle, one that scientists will take up again when the collider restarts in February following a holiday break. Last summer physicists noticed that some of the particles created by their proton collisions appeared to be synchronizing their flight paths, like flocks of birds. The findings were so bizarre that “we’ve spent all the time since [then] convincing ourselves that what we were see ing was real,” says Guido Tonelli, a spokesperson for CMS, one of two general-purpose experiments at the LHC.

The effect is subtle. When proton collisions result in the release of more than 110 new particles, the scientists found, the emerging particles seem to fly in the same direction. The high-energy collisions of protons in the LHC may be uncovering “a new deep internal structure of the initial protons,” says Frank Wilczek of the Massachusetts Institute of Technology, winner of a Nobel Prize for his explanation of the action of gluons. Or the particles may have more interconnections than scientists had realized. “At these higher energies [of the LHC], one is taking a snapshot of the proton with higher spatial and time resolution than ever before,” Wilczek says.

When seen with such high resolution, protons, according to a theory developed by Wilczek and his colleagues, consist of a dense medium of gluons—massless particles that act inside the protons and neutrons, controlling the behavior of quarks, the constituents of all protons and neutrons. “It is not implausible,” Wilczek says, “that the gluons in that medium interact and are correlated with one another, and these interactions are passed on to the new particles.”

If confirmed by other LHC physicists, the phenomenon would be a fascinating new finding about one of the most common particles in our universe and one scientists thought they understood well.

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