Reports are emerging from the Large Hadron Collider at CERN that provide some evidence of the detection of the Higgs boson with a mass of 125 GeV, or about 133 times the mass of a proton.
Why are these reports so tentative? It is because the standards within the high-energy particle physics community for claims of a discovery of some effect are very high. In many areas of research, 5% probability of the result occurring by chance is considered small enough to be worth publishing as a potential real effect. But when it comes to discoveries of new particles, you need to have results that meet the five-sigma threshold, which means that the probability that the observation is not real but merely a product of random chance is 0.000028%. Apparently the current level of confidence in the data is just at the three-sigma level, which implies a 0.13% probability of occurring by chance.
Two independent experiments at the LHC are seeking the Higgs. It is reported that each one is approaching the four-sigma (0.0032% chance) level and once they do, by combining the data to get a larger set and thus improving the statistics, we may reach the five-sigma level.