[This post is now out of date; for a discussion of the data showing strong arguments in favor of confidence, and against confidence, that the excesses in the data reflect the presence of a new particle, click here.]
At 2:30 CERN time today, there was a 90 minute discussion in a room packed with over 100 people, including many experimentalists from the LHC experiments ATLAS and CMS and particle theorists like myself. Not one experimentalist in the room — many of whom actually participated in the Higgs particle searches — used the word “signal” or “evidence”, and every theorist who asked about the “signal” was quickly reminded that an “excess” in a plot is very different from a “signal”. The four experimentalists who spoke very briefly (about the searches for the WW, ZZ and two-photon decays of the Higgs) all made cautionary remarks. There were reminders that the various excesses are still not very significant, and that results are still preliminary and might shift slightly in ways that could increase or decrease their internal consistency with each other. One comment made was that if you re-ran the CMS experiment many times, and there were no Higgs signal at all, you would get (just through statistical fluctuations in the background) two excesses similar to those seen in the CMS two-photon plot 20% of the time. Some very essential differences between the ATLAS and CMS analyses were discussed too. (CAUTION to those who want to naively combine the ATLAS and CMS results! make sure you account for these! Otherwise you will get the wrong answers. And do not add any ATLAS and CMS histograms either.) Various concerns about each analysis, especially the fits to the background in the two-photon searches (which are importantly different in ATLAS and CMS) were voiced during the questions. Much of the discussion was quite technical and very illuminating, focusing on many subtle details (which I have to know about, but most of you can safely ignore.)
What’s the lesson? The experiments have done a fantastic job, and have squeezed the allowed mass for a Standard Model Higgs particle down to a very small range; the hints of a Higgs signal, in each of ATLAS’ and CMS’ search for a particular Higgs decay, are still very faint; and the people who actually performed the analyses, while hopeful to greater and lesser degrees, clearly do not widely believe that the combined case, using all the hints together, is firm evidence of anything unusual — yet.