Once again, there's excitement in the physics community about the possible discovery of the Higgs boson. But this time, it's multiple discoveries...both experiments at the Large Hadron Collider have detected some intriguing possibilities, as has Fermilab's Tevatron. What's going on?
The Higgs boson, just to review, is the only subatomic particle from the Standard Model whose existence remains unconfirmed. Essentially, its purpose is to mediate the mass of all other particles, and by extension, the universe at large. (For more extensive primers, you can go here and here.)
All three of these experiments (Atlas and CMS at the Large Hadron Collider and Tevatron at Fermilab) work by smashing known subatomic particles together - usually protons - in order to create extremely high energies that can allow more exotic particles — including, hopefully, the Higgs boson — to briefly pop into existence. Because the Higgs isn't stable under normal conditions, that's the only way to find it.
Anyway, since the Higgs remains purely theoretical, and we don't know exactly at what energy level it appears, the job of the particle accelerators is to try as many different energy levels as they can, to either definitively rule out some energies or...well, or to discover the Higgs. So far, of course, it's been a lot of the former and none of the latter.
So what's going on right now? Well, the experiments have picked up fluctuations at certain energy levels that might just be the Higgs. One energy excess found by the LHC experiments was at a mass of 145 gigaelectronvolts (GeV), while the Atlas experiment caught another at 250 GeV. Both of those are higher than the current expected mass range for the Higgs, which is beteween 114 and 140 GeV. Tevatron, on the other hand, has found something at right about 140 GeV.
Both of the LHC fluctuations are at what's known as the two-sigma level - in other words, it's two standard deviations away from just being random chance - while the Fermilab result is one-sigma. Two-sigma means there's better than a 95% chance that there really is something at those energy levels, but even 95% isn't terribly convincing to the physics community. A discovery needs to reach five-sigma levels of certainty, or 99.99994% certain, before it can be considered a discovery.
Obviously, we're still a ways away from that, but the recent flurry of potential observations suggests we might be at some sort of tipping point here. If nothing else, even just a year's worth of work from the Large Hadron Collider has ruled out a ton of potential masses for the Higgs, leaving it with very few energy levels left to hide. Fermilab physicist Donald Lincoln appraised the current situation to Cosmic Log:
No reputable scientist is going to tell you anything more than 'this is very, very interesting and we'll keep an eye on it.' But it is indeed very, very interesting. While I'd hate to predict an exact date, it's pretty clear from the performance seen thus and the expected near future that the Higgs will be found or ruled out on a time scale of months or perhaps a year.