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Hectic week December 4, 2008

Posted by dorigo in personal, physics, science.
Tags: , , , ,

The regulars here will have already noticed by now that my posting rate has fallen this week. I have been busy with three different physics analyses, trying to make some progress in each.

The first project is the calibration of the momentum scale in CMS. I have discussed the issue elsewhere a couple of times; I am slowly converging to an understanding of how to treat the Z boson lineshape -which receives contributions from a number of different sources and effects: parton distribution functions in the projectiles, electromagnetic and weak radiation effects, interaction of the final state products of Z decay with the material of the tracker. All this must be dealt with in a coherent fashion to extract the most information possible from the Z decays we will reconstruct in CMS. We have a small but focused group working at the momentum scale calibration, including worthy physicists from Torino University, plus Marco and me. This week, I have tried to determine the effect of parton distribution functions alone, to insert it in our algorithm, but something still escapes me, and I want to do things as well as I can -which sometimes take little extra effort from a mediocre result, but in this case seems to be requiring a lot more care.

The second is the search for Higgs boson decays in the final state arising when H decays to two Z bosons, and one of the Z decays to a lepton pair, while the other decays to a pair of jets. Usually this final state, which is very hard to exploit at low Higgs masses due to the large backgrounds, is used for high-mass searches only (above 200 GeV). We want to extend it to lower masses, where the Higgs is more likely to be, using the Z \to b \bar b decay, which Mia and I have a lot of experience in detecting in hadronic environments. Mia will present some results of this study tomorrow at CERN, so we have been working at this heavily this week.

The third topic is the evaluation of the chances of CMS to detect a similar signature of multi-muon events that CDF has seen in its data. The CDF signal is probably just a not well understood background, but it makes sense to size up the capability of CMS to detect a similar signature with early data. This requires understanding muon sources without using real data, and it is a bit far-fetched, but it is perfectly sound as a masters’ thesis topic, one on which Franco and I in fact have a student working. I have not worked much on this topic this week, but it still has absorbed a little of CPU.

I have a thick agenda of pending things to do, which has grown longer in the last few days. One thing is to post more commentaries on the multi-muon analysis by CDF here. Another is to progress with a document I am writing. A third is to review a 40-pages long CDF paper draft for the Spokespersons Reading Group, to which I proudly belong. A fourth is to organize the upcoming meeting of the CMS-Padova software-analysis group, which will convene in ten days. A fifth is to prepare my next trip to CERN, which will be from next Monday to next Friday. I do hope that I will be able to post more in the next few days… if I survive.


1. Daniel de França MTd2 - December 5, 2008

Did you find the Higgs boson? (Y/N)

dorigo - December 5, 2008

Hah Daniel, I found several tens. The problem is that it is only a Monte Carlo study so far. Once I get the data, I am pretty sure that if the Higgs boson is there, it will pop up in my search channel too. But not before!

2. Amos - December 5, 2008

$10 says he found a signal, and the reason for this blog post was to get us to pay attention to the announcement tomorrow.

dorigo - December 5, 2008

Well unfortunately not… As of today, nobody can announce the discovery of the Higgs boson. Not CDF or D0, since they have insufficient statistics yet. Not CMS or ATLAS, since they have zero stats. So I am glad to bet $10 with you that I do not, in fact, have found the Higgs…

3. Daniel de França MTd2 - December 5, 2008

BTW, my birthday is today. If you have found the Higgs, please, tell me. That would be a great birthday gift :).

dorigo - December 5, 2008

I agree, it would be a spectacular gift to anybody. Unfortunately I am not so wealthy…

4. Daniel de França MTd2 - December 5, 2008

Hmm, Lubos birthday is also today.

dorigo - December 5, 2008

So happy birthday to all the sane and the deranged minds out there!

5. Daniel de França MTd2 - December 5, 2008

“Not CDF or D0, since they have insufficient statistics yet. Not CMS or ATLAS, since they have zero stats.”

Can you tell if any of them as statistics enough to find Higgs using the method you mentioned?

6. Daniel de França MTd2 - December 5, 2008

Sorry, I mean, “enough statistics”.

7. Amos - December 5, 2008

Lol, all I said was “signal,” but if you’re saying you didn’t get even that… Ok. You’ll get the paypal notification in a minute.

8. Amos - December 5, 2008

I can’t find your e-mail address on the site… E-mail me at mine (which I enter each time I post) and I’ll send the 10.

9. dorigo - December 5, 2008

Amos, don’t worry – I like to win uncertain bets, not to strip money off people aimlessly. My email is publically available, but for you I will make the exception of not disclosing it 😉


10. dorigo - December 5, 2008

Daniel, no, H->ZZ production is too rare at the Tevatron to yield a meaningful signal in few inverse femtobarns. The problem is that you usually can discern it only in the ZZ->ll l’l’ final state (l, l’ are charged leptons). The branching fraction of Z->ll is 3.3% for each lepton type, and if you can only see electrons and muons that makes 6.6% for each Z, or 0.4% in total for two Z’s. So only one in 250 H->ZZ can be seen that way… And the H does not always go to ZZ: at most, a quarter of the time.

All in all, a tough channel at the Tevatron, where H production is expected to be a low-rate phenomenon. The larger LHC energy will allow more of such events to be produced.


11. Amos - December 5, 2008

I was actually serious, although I also rather think you were ineligible…

12. Luboš Motl - December 6, 2008

Thanks, Tommaso, for not having forgotten about the sane birthday celebrators, like your humble correspondent. Too bad that you can’t even give us the plain Higgs as a gift. The experimenters are retarded by 35 years or so but it is the theorists who are criticized for this retardation by the deranged role models of yours such as PW. 😉

13. Fred - December 8, 2008

Hi Tommaso & H.B. to Luboš,

This is going off on a tangent, but: who knows, both of you guys might be role models at a White House function one day. I was watching NBC’s one hour political t.v. show “Meet the Press” today featuring Mr. Obama. At the end of his interview, he answered this to the question: “Who are the kinds of artists that you would like to bring into the White House?”

PRESIDENT-ELECT OBAMA: “…Yes, we’re going to have an education policy; yes, we’re going to be putting more money into school construction. … When it comes to science, elevating science once again, and having lectures in the White House where people are talking about traveling to the stars or breaking down atoms, inspiring our youth to get a sense of what discovery is all about. Thinking about the diversity of our culture and inviting jazz musicians and classical musicians and poetry readings in the White House so that once again we appreciate this incredible tapestry that’s America. … I think that our art and our culture, our science–you know, that’s the essence of what makes America special, and we want to project that as much as possible in the White House.”

I’m not going to hold my breath, but it’s a nod in the right direction.

14. Daniel de França MTd2 - December 8, 2008

I just hope Obama ressurect SSC. But I guess this is just a wet dream, don’t you think?

15. Daniel de França MTd2 - December 8, 2008


Here’s some pics of SSC:

The best use of SSC site was as a setting stage for Universal Soldier: The Return.


16. Daniel de França MTd2 - December 8, 2008

SSC website is still online:


17. Daniel de França MTd2 - December 8, 2008

I guess one message was filtered by the spam block.

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