Just this month, the CDF experiment at Fermilab saw a bump in their data at an energy of 140-150 GeV suggesting that they had seen a new type of particle. But does it really exist and, if so, what is it? The result was at the 3.2 sigma level, which in statistics means that it is about three standard deviations away from the null hypothesis--or about a 6 in 10,000 chance that the signal is just a statistical fluctuation. That's a small chance but particle physicists have high standards when it comes to this sort of thing. In particle physics, a 3 sigma result is often described as "evidence" for something but it takes a 5 sigma result to claim "discovery." The trouble is, there are lots of 3 sigma results in particle physics that go away with more data, usually because of some unsuspected systematic error. That doesn't change the likelihood that this result is correct but says that 3 sigma is not actually a discovery, just a promising hint. [Photo court
brought to you by the American Physical Society