Did the LHC Bag a Ginormous New Higgs Boson?

The dawn of a new particle physics golden era? Not quite yet, but still.

Dec 16 2015, 3:53am

Image: CERN

Results presented Tuesday by physicists at the Large Hadron Collider offer the tantalizing hint of a new particle, possibly a very heavy variation of the Higgs boson. Both the ATLAS and CMS experiments, the LHC particle detectors responsible for the Higgs boson discovery, have found significant, unexpected spikes within data representing the energetic aftermaths of super-high energy proton collisions.

The lucky number for both experiments is 750 giga-electronvolts (GeV). It's at this energy that physicists found an excess of photon particles (units of light, basically) within the showers of subatomic byproducts that result when heavier particles (like protons) are smashed together and annihilate. (The green lines in the illustration below would be photons.) Some of these byproducts exist for barely any time at all, but their existence can be inferred by looking for energy spikes such as this.

Image: CERN

If the results are confirmed by further data, they would indicate the presence of a new particle of around 1,500 giga-electronvolts produced in proton collisions and decaying almost immediately into two of photons of 750 GeV apiece.

And the results do absolutely need confirmation. The statistical bump found by the ATLAS comes with a significance of 3.6 sigma, while the CMS group wound up with a 2.6 sigma excess at 750 GeV. These are not slam dunks by any stretch. In particle physics, 5 sigma is the standard for a discovery, corresponding to about a 0.00003 percent chance that the results happened just by dumb luck. A 3 sigma result, which is usually taken to indicate evidence of a discovery but not an actual discovery, means that there's about a 3 percent chance that the results could have occurred via dumb luck. A 2.6 sigma is not even evidence but it's also not nothing-nothing.

(An interesting thing: The chance that a result could have happened by dumb luck is always there, even if it is approaching the infinitesimal.)

More concretely, the CMS group registered 10 750 GeV events, while the ATLAS group nabbed 40. As noted in Nature News, the excesses would be completely unremarkable had they not occurred in tandem at separate detection experiments. "It is a little intriguing," ATLAS spokesperson Dave Charlton told the journal. "But it can happen by coincidence."

French physicist Adam Falkowski, who'd been hinting about Tuesday's results on Twitter several days ago, has a good analysis at his Resonaances blog. For one thing, he contrasts the latest data spikes with what was seen of the Higgs boson three years ago. Then, unlike now, the interpretation of photon pairs (a diphoton) at 125 GeV was reasonably clear and shared by most physicists: the Higgs boson. A 1,500 GeV diphoton, however, could be any number of things, including one of several theorized additional Higgs bosons. That ambiguity adds a whole new level of excitement.

"Most likely, this particle would just be a small part of the larger structure, possibly having something to do with electroweak symmetry breaking and the hierarchy problem of the Standard Model," Falkowski writes. "If the signal is a real thing, then it may be the beginning of a new golden era in particle physics."

In any case, we will know more for sure when the next round of LHC data starts rolling in in 2016.