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CDF Sees Evidence for Single Top August 14, 2007

Posted by gordonwatts in physics.
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At last Friday’s Fermilab Wine & Cheese CDF showed slides in which they crossed the magical 3 sigma threshold for observation of single top: Evidence! They have two analyses — the Matrix Element and the Likelihood Fit. The Matrix Element is at 3.1 sigma, the Likelihood is at 2.7 sigma. The main change since their last result seems to be a substantial increase in the size of their data set (1.5 fb-1).

That must have been a lot of work! Congrats!

D0 is not updating its results for this round of conferences — so we remain at 3.5 sigma.

The Matrix Element shows a steady increase in sensitivity that is understandable. But I’m curious to know what happened with the likelihood. Back at the end of 2006 it showed no sensitivity in the 1 fb-1 version of the analysis (reported an expected limit, and the observed limit was even tighter than the expected one), but now has almost 3 sigma expected sensitivity. Were they just unlucky before and lucky this time? Or did something fundamental change? Unfortunately, this talk is not the talk to describe this — Mark’s job was to present all the recent new results in 45 minutes; so no time for details!

UPDATE: It was pointed out that we are now at 3.6 sigma, not 3.5 sigma. Ops!

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1. Andy - August 14, 2007

See slides 54-63 of his talk… (in the backup)

Likelihood analysis now has:
– improved treatment of kinematic
ambiguities
– Bug fix in matrix element
– More MC statistic allows refined
training

Also, both analyses now:
– have new ALPGEN Monte Carlo
– do W + Heavy Flavor normalization from W + 1 jet events

Not being an insider on their analysis, I can only guess which of these made the most difference, but “bug fix in matrix element” could have a large effect.😉


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