I let a few weeks pass before pitching in on this, now that fewer eyes are looking. What I really would like to know is the details of the modeling of the QCD background, the fat red histogram that is responsible for the shape of the falling spectrum at high reconstructed mass.

Because, if I am not mistaken, the fact that you now see no excess is due to a remodeling of the QCD background (which used to be quite a bit leaner in the 1/fb analysis). So I really wonder, was it really a statistical fluctuation or a systematic underestimate of the background ?

Sorry for being quite direct… I decided not to post on this issue in my blog and just ask you here. If the new QCD model is better than the old one it is entirely to your credit, not the other way round. I think you, Anton and the others did a terrific job and I cannot see a way to improve the analysis.

Cheers,
T.

I’m confused. If I look at the paper you linked to describing this analysis
I see that the combined efficiency listed for a 90 (250) gev higgs is 1.0% (3.1%).
And the cdf higgs webpage has a paper describing the 1.0/fb analysis which
lists the combined efficiency for the same masses as 1.1% (3.3%). Also, the
ratio of the total number of predicted taus faking jets in the two analyses is 1.6 (slightly less than the 1.8 that comes just from luminosity scaling).

So it doesn’t appear that a looser event selection has led to increased predictions for the signal or the fake background. However, as I wrote in my previous post, it looks like the prediction for the jet faking tau background in the mass region the excess was observed in the 1.0/fb analysis has increased by 3.5 instead of 1.8. Did I misunderstand your answer?

Eric, #25, apaprently you didn’t read my original posts. I think if you go back and do your homework, you can tone down the sarcasm a bit. I never hyped anything…the media did. It was a typical cycle with this sort of fluctuation. The main point is if the Higgs *had* been there this is *exactly* how it would have appeared. My first post, and this one, was all about how important it is to remain skeptical, while being human. This is exciting! Are you saying you never expect to see a Higgs anywhere?

In response to your comment #28, our estimate of the probability of a fluctuation *of course* took into account that a fluctuation could have been anwhere. This was discussed in the first posts, which, as I say, you really should take the tme to read. I stand by every word I wrote.

A 3-sigma effect is decent, but any good particle experimentalist will tell you that 5 sigma is the gold standard. Many people (especially theorists) ask: a 3-sigma fluctuation is so statistically unlikely already–why need 5? The answer: Well, the probability of a 5 sigma is exponentially suppressed compared to 3 sigma. But more saliently, it also offers robustness against mistakes in error estimation. For example, if you accidentally underestimate your error by a factor of 2, your great 3-sigma effect now becomes a 1.5 sigma effect, which happens quite frequently. Similar reasoning applies to error estimation from Monte Carlo, which may not properly model new physics, etc.

The point of having 5 sigma is so that claims of discovery are robust against not only statistical fluctuations, but also against experimenter-related mistakes. Until one is near that, I think it’s misleading to imply a near-discovery (as it seemed to me was done here at CV, New Scientist, etc.) There was no legitimate reason to hype up the result so much.