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The MSSM Higgs signal buried in my plot March 1, 2007

Posted by dorigo in internet, news, personal, physics, science.
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Maybe a few readers of this blog will remember my comment of the recent 2.1-sigma excess of H->tau tau candidates found by a CDF analysis looking for MSSM Higgs bosons  (also see  the followup with the D0 search of the same signal ). In it, I hinted at the intriguing coincidence of the CDF excess of tau-pairs – whose combined mass pointed at a possible MSSM Higgs boson of 160 GeV – with some disturbance in a D0 plot of their Z->bb excess (see graph on the left, where the points represent a deviation from the best fit) which could again be attributed to H->bb decays, and added half-jokingly that the much larger-statistics Z->bb signal about to be approved by the CDF collaboration was going to show the same trend.

Now, after the blessing of the Z signal by CDF , I can discuss openly the matter. Indeed, I at least owe it to Anil Ananthaswamy, a reporter from  New Scientist, who contacted me to discuss my post on the 160 GeV excess and to get more information from me. Although I discussed the matter in detail with him, I did not give him any insider information on the CDF analysis beforehand, because I am determined to follow the rather strict rules that my experiment has set to its collaborators. But I also promised I would answer all his questions in due time.

Here are some of the questions that were raised, with my answers [Between square brackets some of my additional editing].

 

Q: What is the difference between your search and the search that was carried out by John Conway’s team (Higgs->tau pairs)? Were you also searching for a MSSM Higgs?

A: No. We have been searching for a Standard Model signal, the Z->bb decay.
The difference with the MSSM search of H->tau tau is that the final
state is different, and that we have tried to see a very well known signal
to extract a calibration of jet energy, while John’s group has been
searching for physics outside the Standard Model (MSSM) from the outset.

Q: What is the nature of the deviation that you have found? And at what mass scale have you found it?

A: We have not found any significant deviation, in the sense that physicists attribute to the word “significant”. What the mass spectrum we are publishing today shows [see picture on the left, better seen in another post ] is that we understand the data well, and any discrepancy from our model is understandable as a statistical fluke. However, if there were a SUSY Higgs boson at 160 GeV, then our plot should contain maybe a hundred of those events. A hundred events at 160 GeV of mass would be impossible to see with certainty, but our plot does not rule out that possibility either – and actually there is an upward fluctuation of the data right at about that mass value, of the size one would expect from MSSM [see blowup of region around 160 GeV, where the “excess” of data – the blue points – with respect to the fit is shown].

Q: How significant is this deviation?

A: Not tested yet, but probably less than one standard deviation. [One should remember that plots such as the one shown here do not include systematics on the background shape parametrization, which would easily eat up the upward wave at 160 GeV.]

Q: What did you think when you first saw this deviation? Knowing that Conway’s team has also seen a 2-sigma deviation, what do you think is going on when you look at both results?

A: I have always considered the possibility that a new resonance could
show up in a b-bbar mass distribution which also contains a clear signal of
Z->bb decays. But I have also known that it would be quite hard to see it first in this final state, due to the large backgrounds. When I saw the fluctuating points around 160 GeV I did not think much, nor do I now. But I know several colleagues who could take the three pseudo-signals, D0’s one, Conway’s 2-sigma one and my fluke, and take that quite seriously. However, I am not as easily excited, and I still believe it is a fluctuation in Conway’s plot and another fluctuation in my plot.

Q: You had mentioned [in the past] that you think the standard model is right.  Given the latest data from your work, do you still think the same?

A: Yes. And extraordinary claims need extraordinary evidence, so – after
thirty years of incredibly precise confirmations of the Standard Model –
we need a HUGE signal of new physics before I get convinced there is
something beyond. Make Conway’s signal a 5-sigma one, and I will still
believe the SM is right and there is something wrong with that analysis.
Only after a very careful scrutiny and independent checks could I get
convinced.

Comments

1. Dick - March 2, 2007

In the March 2007 Scientific American, page 22, a news article reports that the CDF collaboration’s new weighing of the W mass pushes the upper limit of the Higgs mass to 153 GeV. Doesn’t this exclude 160 GeV as a possibility? (The article also quotes you, but on another topic.)

Dick Dolan

2. Jester - March 2, 2007

Tommaso, do you know why those people call it the MSSM higgs signal? Is it just that it cannot be the Standard Model higgs so they deduced it must be the MSSM? Or is there something more to it?

3. Andrea Giammanco - March 2, 2007

Have you read this?
http://www.newscientist.com/channel/fundamentals/mg19325934.600?DCMP=NLC-nletter&nsref=mg19325934.600
(I’m sure that this comment will be filtered out by your anti-spam, since it contains a URL, so don’t forget to unblock it…)

“Meanwhile, another team led by Tomasso Dorigo of the University of Padua, Italy, has been independently analysing an entirely different set of particle interactions seen by the CDF experiment and it too has found hints of some unknown particle at 160 GeV.”

Hmmmm, I suspect that there are at least three mistakes in this sentence… (Name, institution, and role!)

4. Andrea Giammanco - March 2, 2007

no, sorry, the institution is correct (for some reason I had read Pavia instead of Padua)

5. John Conway - March 2, 2007

Tommaso, we’ve excluded already a Higgs that would have given you a hundred events…I also added a comment to this effect on your “Just Blessed” post.

If you had had an excess equivalent to the tau pair one, you’d only get about 20 events, spread out over as many bins.

– John

6. John Conway - March 3, 2007

Oops.

I take it back – there should be more like 400-500 events if there is a Higgs signal around 160 GeV.

My fault, I was going too fast!

So, Tommaso, shouldn’t we quickly turn this into a Higgs limit?

I suppose the mass spectrum shape systematics are tricky, but let’s discuss!

– John

7. dorigo - March 4, 2007

Hi Dick,

thank you for pointint out the Scientific American article. I have been unable to see it yet, am on vacation right now… Will have a look when I am back!

As for your question: no, it does not rule it out. First, because 153 GeV is a 95% upper limit, which means that 5% of the times things go awry by default. Second, because we are talking about a MSSM signal here, which has different properties…

Cheers,
T.

8. dorigo - March 4, 2007

Hi Jester,

well, if it was a SM higgs, then it would have a rate that is way too high. It would just be a fly in the face of the Standard Model.
Instead, as a MSSM neutral higgs, the rate would be reasonable… And indeed, the analysis which aimed at excluding a region of the mass/tan beta plane was unable to exclude the region at M=160 GeV, tan beta=40 as it was supposed to, because of the excess.

Cheers,
T.

9. dorigo - March 4, 2007

Hi Andrea,

well, they can say I led the group, in the sense that I have been doing this for 10 years now. Technically, though, the team leader since late 2005 has been Julien Donini. I have been the mastermind though🙂

The name is wrong but I am getting used to it😦

I will now give a look at the link, thank you!
T.

10. dorigo - March 4, 2007

Hi John, thank you for your visit here.

I do think there is some potential for limit-setting in the Z->bb dataset. However, it is going to be quite hard, because of two things:

1) the background shape is modeled using data failing some “Z-tuned” kinematic cuts. If the H->bb is there too, the cuts are less efficient in selecting it out, with the effect that the background model “eats out” a bit of the Higgs signal. That is because the H likes to be produced by gluons yielding top loops in the initial state, with the effect of larger initial state radiation… But you know more than me on this: is there any difference in the MSSM production processes, as far as ISR is concerned ?

2) the systematics of the background are a nightmare. We would need to run a ton of QCD MC and try to do the background with that. If we did it, though, maybe the Z sample could indeed yield some limit for the MSSM.

I look forward to discussing the matter with you.

Cheers,
T.

11. Dzero's new limits on SM Higgs cross section « A Quantum Diaries Survivor - April 23, 2007

[…] Associated WH or ZH production is in fact another important means of producing Standard Model Higgs bosons. You search for a signal of the leptonic decay of the W or the Z, while this time you try to detect the decay to jet pairs of the Higgs. Of course, the Higgs is  not forced to choose to decay to b-quark pairs if produced with a W and a Z, and to decay instead to two W bosons in case it is produced alone! Rather, D-zero searches for the two b-jets signature in WH and ZH production, and not in H production alone, because identifying a pp->H->bb signal by itself would be almost hopeless due to the huge concurring backgrounds from pp->gluon->bb (but see a discussion of that issue here ). […]

12. scott - October 13, 2008

an alien on this forum said

http://alienhub.com/showthread.php?t=2510&page=2

What your scientists are searching is the element that gives the force to the mass. You call it boson of Higgs. This particle has a charge of 153 GeV, so the Large Hardron Collider will not prove its existence. The greatest feature of this particle is the resonance that he can have with a sincronized particle anywere in the universe. The particle is anywhere, and you can teleport any materia or transfer any data using this principle. This is possible because the force of this particle is non-0 anywere, whatever the distance. If you calculate it, this value will be always >0,this respects the G force formule, and becomes weak as distance grows. It is the base of our technology, and of our data share.

13. 18 months after the Higgs affair… « A Quantum Diaries Survivor - October 28, 2008

[…] would not appear. In fact, some colleagues in CDF were not happy with the blogging John Conway and I had done about the issue, and we were identified as the source of the trouble with the New Scientist and […]


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