Physicists have uncovered what looks like a quantum conspiracy in one of the first results from the Large Hadron Collider, the world’s most powerful atom smasher.
A larger than expected number of charged particles generated during the LHC’s highest energy collisions are doing something they have no business doing. Instead of flying away from the collision site in random directions, these particles are somehow paired, moving away from the point of impact at similar angles and ending up at opposite ends of the collider’s CMS detector.
It’s as if some of the particles “managed to talk to each other” immediately after their creation and stayed in contact while zooming off in opposite directions at close to the speed of light, says Gunther Roland of MIT, a collaborator on the collider’s compact muon solenoid experiment. There’s no obvious explanation for the puzzling finding, he adds.
Roland and Guido Tonelli of the University of Pisa and the National Institute of Nuclear Physics in Italy presented the results September 21 at CERN, the European physics lab that operates the LHC near Geneva. The researchers and their colleagues also posted their findings September 22 on arXiv.org.
The team made the discovery, never before seen in interactions between energetic protons, after analyzing some 350,000 high-intensity collisions recorded between this past March and August, when the collider’s twin proton beams reached half their maximum energy. Among high-energy proton collisions that generate 100 or more charged particles, only a few percent of the particles show the correlation effect, Tonelli says.
Although the effect is small, the number of paired-off particles is significantly higher than expected, notes Roland.
And try as they might to find an error in their analysis that could eliminate the unexpected particle pairings, “we didn’t succeed to kill it,” read one of the slides Tonelli presented during the September 21 talk.
The correlation between particles almost certainly has something to do with quantum chromodynamics, the theory that governs the strong force between subatomic particles such as protons and neutrons in the nuclei of atoms, but it remains unclear exactly what facet of the theory provides an explanation, Roland says.
Theorist Larry McLerran of the Brookhaven National Laboratory in Upton, N.Y., suggests that the pairing off of high-speed particles is evidence that enough nuclei are traveling close to the speed of light at the impact site to create a proposed, ultradense type of matter known as a color glass condensate. Color refers to a type of charge carried by quarks and gluons, some of the basic building blocks of matter.
The interactions of the condensate are accompanied by enormously strong color fields that are analogs of electric and magnetic fields. These fields could cause particles to pair off in the pattern observed at the collider, much as a random scattering of iron filings lines up when a magnetic field is applied, says McLerran. He and other researchers have invoked a similar explanation to account for the pairing off of particles created when heavy ions smash into each other at high energies in Brookhaven’s Relativistic Heavy Ion Collider.
