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Just Blessed!!!!!!! February 23, 2007

Posted by dorigo in news, personal, physics, science, travel.

Julien blessed our new result of a Z->bb signal from Run II CDF data.

We measure a signal of 5674+1540-725 events, and a b-Jet energy scale factor of 0.974+0.020-0.018. The latter is the most precise and only determination of this quantity so far. It basically tells us the amount of miscalibration of our jet energy corrections for b-jets.

Using the b-JES for the reduction of the top quark mass systematic uncertainty will require more work. But today’s step is a long and important one. We expect that most of CDF top mass determinations will benefit from it.

In the plot below, hot from the press, you see as blue points with tiny error bars the dijet mass distribution of experimental data after a tight selection aimed at increasing as much as possible the elusive Z signal. The black curve is the fit, the fitted Z signal is in red, and the QCD background is in green. In the inset you see the excess of data over the background alone, compared to the fitted Z signal.

Tomorrow I am on a flight to Madrid, Mexico City, and Cancun. I will arrive in Cancun on Sunday at 11AM, and from then, I will relax for 10 days on a nice villa in the mayan riviera. Having the blessing of the Z signal behind my shouders will make it an even sweeter vacation!


1. Tony Smith - February 23, 2007

Thanks very much for posting the blessed CDF Z-> bb plot.

It seems to resemble very closely the D0 plot, including what you had described as “… an excess at 160 GeV … a bump at 160 GeV …”, when you take into account shifting the mass scale so that the Z peak is at the accepted value of the Z mass.

Since D0 and CDF not only do independent analysis work, but also take independent data sets, it seems likely to my naive mind that the “bump” around 160 GeV should be something real.

Would realistic statistical arguments agree with the conclusion that the bump is probably real ?

If it is real, what would it be likely to be ?
Are W pairs ruled out as already being included in background calculations ?
Could it be the first sighting of the Higgs ?

Enjoy the Mayan riveira. I hope the weather is good.

Tony Smith

2. Kea - February 24, 2007

Congratulations! And I must say I’m very impressed by the clarity of the diagram, even down to the choices of colour. Do you have a ballpark timescale on new top quark mass uncertainties?

3. dorigo - February 24, 2007

Hi Kea,

thank you for the kind remarks… The details of the plot have been chosen by Julien, and his is the merit (I did give a few suggestions, to be fair).

Top mass measurements released now or about to be released for winter conferences will not use the new measurement of the jet energy scale. I hope that starting with summer 2007 results we will see analyses using the information we extracted. However, there is some work to be done on understanding the extrapolation from jets in our dataset and jets used for top mass reconstruction. Not much anyway.


4. dorigo - February 24, 2007

Hello Tony,

I want to address your questions in a separate post, since they also address the issue of the 160 GeV Higgs “signal” found by CDF.


5. Andy - March 1, 2007

Congratulations, Tony.
I did the Z->bb analysis at D0, so I know how much work goes into this.
As for the 160 bump, looking at your plot, I don’t see any.

6. dorigo - March 1, 2007

Hi Andy,

thank you! (My name is Tommaso, Tony is a welcome commenter here).

I agree, there is nothing real in my plot – but indeed, there could be space for 100ish events at 160 GeV, take a look at my post from today where I have a blowup of that region😉


7. Another Higgs bump? Not so fast… | Cosmic Variance - March 2, 2007

[…] 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 […]

8. John Conway - March 2, 2007

Tommaso, congratulations, nice analysis! But as for a Higgs signal, do the math – your analysis has no sensitivity for a Higgs signal at the level of the one seen in the tau pair analysis. We’ve already excluded what you might have been able to see!

See my post over at Cosmic Variance



9. dorigo - March 4, 2007

Hi John,

I agree with you – but only after we take in consideration background systematics (which can be perfected, by the way). Indeed, the rumors of this MSSM Higgs have been exaggerated – but ain’t it nice ? We at least get the interest for this thing going!


10. Borborigmi di un fisico renitente » Ancora tracce del bosone di Higgs? Il sottile confine tra le chiacchiere da bar e la dichiarazione pubblica - March 12, 2007

[…] (Dorigo) fa qualche alluzione un po’ azzardata: se nei dati di Conway ci fosse veramente il bosone di Higgs, allora dovrebbe fare capolino anche […]

11. A new physicist on the scene « A Quantum Diaries Survivor - May 29, 2007

[…] of her daughter Madeline Jane. Chris has worked with me in the group that recently produced a new measurement of the b-jet energy scale from a fit of the peak of Z decays to b-quark pairs. He gave an important contribution to our work […]

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