This past winter a combined analysis of data from the two Tevatron experiments showed at 95% confidence level that the Higgs mass could not be in the range 160-170 GeV. This was a better result than expected: statistically the experiments should not have been able to exclude any of the mass range, but were helped by a downward statistical fluctuation.
Today a new and improved combined analysis was released using more data, and the new result is that there has been a reversion to the mean, no more help from statistical fluctuation downwards. Statistically, this time they should have been able to exclude 159-168 GeV, but now the fluctuation is a bit upwards, so the actual exclusion region is 163-166 GeV. In essence, better data has shown that the likelihood of a 160-163 or 166-170 GeV Higgs, something that was previously assigned a probability of a bit less than 5%, now has a probability a bit more than 5%. So, any putative Higgs particle in those mass regions has now escaped being tarred with the unfair label of “excluded”.
If the Higgs is actually there at a certain mass, as one gets closer and closer to having sufficient data to exclude its existence, one should find oneself doing nowhere near as well as expected as far as excluding that mass. A thoroughly irresponsible person might see some significance in the fact that, unlike the analysis from earlier this year, the new improved analysis with more data does a worse job of exclusion than expected over much of the low mass range, peaking at 1.5 sigma or so for the mass range around 135 GeV.
Update: More detail and rank speculation about this from Tommaso Dorigo here.
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