Is Particle Physics About to Crack Wide Open?

Hints of an unexpected new particle could be confirmed within days—and if it is, the Standard Model could be going down.

Scientific American, By Michele Redi, June 13

It’s December 15, 2015, and an auditorium in Geneva is packed with physicists. The air is filled with tension and excitement because everybody knows that something important is about to be announced. The CERN Large Hadron Collider (LHC) has recently restarted operations at the highest energies ever achieved in a laboratory experiment, and the first new results from two enormous, complex detectors known as ATLAS and CMS are being presented. This announcement has been organized hastily because both detectors have picked up something completely unexpected. Rumors have been circulating for days about what it might be, but nobody knows for sure what is really going on, and the speculations are wild.

The CMS spokesperson takes the stage first, giving a presentation with no surprises until the very end, when two plots appear showing the energies—theoretical and actual—carried by a flood of particles emerging from head-on collisions between protons traveling at nearly the speed of light. If you squint, there appears to be bump in the experimental curve, suggesting too many events at one point than theory would predict. It could be evidence for a new, unexpected particle—but at a level that’s merely interesting, not definitive. We’ve seen things like this before, and they almost always go away when you look more closely.

Then Marumi Kado from ATLAS steps up, with a strangely confident look in his eye—and when the results finally flash on the screen, the audience understands why. ATLAS has seen the bump too, at the same point as CMS did, but now it’s so prominent that you can’t miss it. This really does look like a new particle, and if it is, there is suddenly an enormous crack at the very heart of high-energy physics.


The importance of this result is clear to everybody working in the field and it has immediately triggered a huge amount of work on the possible implications. None of the more fundamental models that currently exist as possible replacements for the SM can explain the bump. If the SM has fallen it is likely not for any reason we expected. If the new particle is real, it is absolutely unclear what might be its role in the greater scheme of things. Maybe it is related indirectly to the Higgs boson somehow, or maybe it is connected with the puzzle of dark matter in the universe. Or maybe it is just there by chance. Certainly these are questions that scientist will have to answer in the future and more data will help to understand what lies ahead.

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