Another Higgs bump? Not so fast…

By JoAnne Hewett | March 2, 2007 8:12 pm

The New Scientist has picked up my story of the Bump Hunt in their issue this week. The author, Anil Anathaswamy, interviewed me for an hour a couple weeks ago on the phone, wrote a draft, let me look it over for fact-checking. By and large he got the story correct, I’d say. It’s an odd feeling, though, I have to say, to se it out there like that.

The article was also provocative about the possible bump in the Z to bb analysis from CDF, which, now that it has been approved, is public. Tommaso Dorigo’s blog has a more in-depth look at that. But I think that is even more of a stretch than our two-sigma excess. The reason is simple: suppose our excess is in fact the beginning of a Higgs signal. You can ask the following obvious question: if we have a certain rate in the tau lepton pair channel in our analysis, what would the rate be like in the bb mode that Tommaso studied? Can they even see such a thing?

We can answer the question ourselves without doing a lot of work, by making a simple assumption. In both analyses, we are looking for a signal which is a small bump centered at 160 GeV or so, on top of the falling spectrum for events with masses larger than that of the Z boson, which appears in both analyses as a much larger bump centered at the Z mass, 91.2 GeV. In the tau pair case the excess is about 15 events, compared with about 250 Z events. So what does that imply for the bb case? We can assume that if there is a signal, the ratio of Z events to Higgs events is the same, but then also you need to take into account the different branching ratio to the bb final state. For the Z, the branching ratio to bb is 5.6 times bigger than the tau pair ratio, and for the Higgs it’s about 10 times bigger. So in the bb analysis, the ratio of Higgs to Z events is 1.8 times bigger than that in the tau pair case. You still with me?

Now, the bb analysis (which is quite a nice piece of work by the way) has about 5600 Z events, or 200 times more than the tau pair case. (It’s much easier to see these sorts of events than tau pairs, in case you are wondering…) So, if the tau pair excess is real, they should expect 1.8 x 5600 x 15/256 events, or on the order of 400-600 events, spread out around 160 GeV in mass. It would be about 10% as big as the Z peak.

It’s pretty clear that the data don’t really show such a peak…

The bottom line is that the New Scientist article, though provocative, overplays this non-signal, and so does Dorigo himself, I think. Sorry Anil! I should have looked into this earlier.

Otherwise, they’d have supersymmetric Higgs limits much like the tau pair ones, right? We’ve already excluded anything they can see in the bb analysis…but they should do the limit!


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