Researchers at CERN and the world over were already sure they had found the Higgs Boson - five-sigma sure - but in case there were any lingering doubts a new round of results coming out of Geneva further backs the earlier findings. One team there now reports a 5.9 sigma level of certainty that the Higgs exists. That equates to a one-in-550 million chance that the results are incorrect reflections of statistical errors.
The agreed-upon sigma level for a proper discovery is a 5-sigma result, which only requires a one-in-3.5 million chance of statistical fluke. That's what both the ATLAS and CMS teams were claiming back in July when the initial discovery was reported (technically CMS was reporting a result between 4.9 adn 5 sigma). The ATLAS team has now submitted additional data on the "decay channels" by which the Higgs breaks down into lighter particles a fraction of a second after being created by high energy particle collisions. The CMS reiterated its 5-sigma certainty in the same journal (Physics Letters B).
What does that mean? Well, it means that we were already really sure about the Higgs, and now we're even more sure. But there's still a lot we're not sure about, like whether the Higgs that we've found is actually the Higgs that we've theorised about, the one that fits perfectly into our Standard Model of the universe. That's going to take a lot more science. But at least we can be nearly 6-sigma sure that we've found something very interesting.