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Evidence December 9, 2006

Posted by gordonwatts in physics.

CIMG9576But I notice not that public yet (what is with our experiment!? Too busy, I guess, producing good physics! ;-). 3.4 sigma!

Dugan gave a great Wine & Cheese seminar and announced the results. I don’t have the final copy of his talk, or I’d post it here. The place was packed with people (sitting in the aisles) and Young-Kee got the lab to buy some fake bubble and gave us a nice toast at the end of the talk (thanks – I know that isn’t normal procedure, but I think the lab should do more things like that in the future!). In summary:

  • Three methods to search for single top production on a common dataset: Decision Trees, Matrix Element, and Bayesian Neural Network. Listed in order of decreasing expected significance as measured on zero-signal ensemble tests.
  • The DT sees single top with a significance of 3.4 sigma, the ME is 2.9, and the BNN is 2.4. All measured, again, on the zero signal ensembles.
  • As several people from CDF pointed out (repeatedly :-)) we were amazingly lucky. Our DT’s expected significance is about 2.1 — we see 3.4. Of course we measure a high cross section: 4.9 + 1.4 – 1.4 pb. CDF has an expected sensitivity in their best analysis of 2.5 sigma. They were unlucky, however, and saw only 2.3 (I’m recalling those last two from memory). So CDF has, if we measured sensitivity the same way, a better analysis, but we have better data. I guess we at DZERO need to be a little bit humble about that (even though that is hard to do sometimes!).

Afterwards there was a party. We started a bar tab and invited all of Fermilab to come. I took some video (to come later) and some pictures. But the pictures don’t do the get together justice: I forgot about my camera and didn’t start taking pictures until just before I had to leave: a number of people had already left.

As Aurelio pointed out: this is just the start for both experiments. We’ll combine and extend our techniques, get to the 5 sigma range, and then do the thing we really want to do: start measuring its properties!

Perhaps I missed it, but I don’t see an announcement, and I don’t see a copy of Dugan’s talk posted yet. A PRL is coming after that, and since that isn’t the most useful thing for an analysis this complex, a PRD is coming soon after that. And we thought making this announcement would give us some breathing room!



1. Dynamics of Cats - December 14, 2006

top that

From Gordon via Chad Fermilab is claiming single top quark decay to b quark + W ie the accelerator produced a t-quark as part of some quark/anti-quark ensemble, without simultaneously producing and anti-t-quark….

2. dorigo - December 16, 2006

Hi Gordon,

Tony Smith would like to have a few details of your decision tree. Have you followed his questions (to me) about your analysis in my blog ? I answered to the best of my knowledge, but I guess there would be interesting details to add to the picture. I encouraged him to talk to you and Gustavo about it, but I guess he has not done so yet.

In a nutshell, would your analyses be sensitive to the single top production process if the top quark mass were sizably different from 175 GeV ? Like 145, or 205 ?


3. gordonwatts - December 18, 2006

Hi T – No, I’d not seen your post. Work has been hell what with this and other things; I’ll follow up on it. -Gordon.

4. gordonwatts - December 18, 2006

The short answer is probably not. Or certianly, less so. We have the top mass “hard-coded” into various bits of the analysis — the single top MC for the training samples for the DT and BNN analyses. And the top mass in the ME analysis.

5. CDF Sees Evidence for Single Top « Life as a Physicist - August 14, 2007

[…] is not updating its results for this round of conferences — so we remain at 3.5 […]

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