US researchers tantalizingly close to Higgs boson “evidence”

Researchers at the Tevatron particle accelerator in Illinois say they’ve come about as close as you can get to finding evidence of the Higgs boson particle. The announcement comes amid rumors that researchers at the Large Hadron Collider will make a notable announcement this week.

At the moment, the Higgs boson is still hypothetical and largely based on the idea that if it did exist and had certain characteristics, wider theories of how particle physics work would make sense.

Coverage of the work so far has generally used the analogy of “hunting” for where the Higgs boson is hiding. In reality, this has meant running experiments based on it having a range of possible masses. “Finding” it would not mean literally spotting it, but rather detecting its effects.

So far the search has been the slightly odd case of “no news is good news.” As each experiment comes back without “success”, scientists narrow the range of masses at which it might exist, thus meaning we get ever closer to the point of either finding that it does exist or having to conclude it likely doesn’t exist and having to have a major rethink of particle physics.

The LHC project has worked on the basis that the Higgs boson has a mass measurable between 115 and 135 Gigaelectronvolts (GeV). Last December two separate LHC experiments narrowed down the likely range to 125-126 GeV, though that was later revised to 122.5-127.5 GeV.

Now researchers on Tevatron (pictured) have released their final findings from data produced before the accelerator ceased operations in September thanks to budget cuts. They report that it’s likely they have actively inferred the Higgs boson’s existence at 125 GeV (as opposed to showing it doesn’t exist at any other mass).

Depending on the calculation you use, and whether you put extra weight on Tevatron producing the same result from two different experiments, the chances of the result being down to chance is somewhere between one in a few hundred and one in a thousand. The best non-scientific explanation comes from Rob Roser, who worked on the Tevatron project and told the Wall Street Journal that “I’d be willing to bet your house it’s real but not enough to bet my house.”

The level of confidence that physicists have in their results being accurate rather than a freak occurrence is stated in sigma. Tevatron signal of the Higgs boson existing is rated at around a 2.9 sigma level. In terms of being “official”, a signal has to be rated at 3 sigma before it can be formally labelled as evidence. It takes 5 sigma (a one in a million probability of the result being chance) before signal formally becomes a “discovery.”

Officials at CERN, home to the LHC, are rumored to be preparing to make an announcement tomorrow. The speculation is that this will be that they have also detected a signal of Higgs boson rather than just narrowing down its likely range. If this turns out to be at 3 or even 5 sigma, it may mean that even though Tevatron “spotted” the Higgs boson first, LHC gets the official credit for finding evidence or even discovering it first.