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Scientists at CERN are being a little gun-shy even as it appears that they'll announce they have proof of the Higgs boson—the building block of all matter—but are stopping short of calling it a "discovery." As The Associated Press' John Heilprin and Seth Borenstein report, "experts familiar with the research at CERN's vast complex on the Swiss-French border say that the massive data they have obtained will essentially show the footprint of the key particle known as the Higgs boson—all but proving it exists—but doesn't allow them to say it has actually been glimpsed."

"Discovery" is a touchy word in physics, especially when it comes to Higgs. As we noted last month, there's a scientific threshold called 5-Sigma that scientists use as a benchmark to prove that they've discovered something. And back then, there were rumors that experiments of the Higgs resulted 4-sigma signals (as our commenters have pointed out, it's about a 110x difference but is better than the initial 3-sigma "in excess" which prompted the first round of rumors), and scientists were speculating whether or not these multiple 4's would trump a 5-sigma and perhaps trigger "discovery," and how exactly CERN would spin it.