At this week’s Hadron Collider Physics Symposium, the CDF and D0 experiments at the Tevatron announced their newest results on the search for a standard-model Higgs boson. You can find documentation from the two experiments here, and this is what the “money plot” looks like:
The mass range 163-166 GeV is excluded at 95% confidence level. Now, for comparison, here is what this plot looked like in March:
At that time, the exclusion range was stated as 160-170 GeV. More data, but the excluded range got smaller? Indeed so. However, the real figure of merit for the reach of the search is indicated by the dotted line on both plots, which indicates how well you expect to do. This is what is used to design the data analyses — not what you get from the data themselves, as looking at the actual data can bias your results. As of March, we would have expected not to be able to exclude any Higgs production at all, and lucky (or unlucky?) fluctuations made the data look more background-like than Higgs-like, and thus the experiments were able to set a limit. But now the dotted line is lower on the plot, and below the standard-model line over a small region, so now it is expected that we set a limit, and the data are consistent with that…but the actual observed limit has gotten worse. As we like to say, you get what you get.
Fermilab will continue to take data and improve these limits — or, for all we know, discover a standard-model Higgs. The turn-on of the LHC, which is expected to continue this weekend, will bring more players into the game.
