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CDF publishes multi-muons!!!! October 31, 2008

Posted by dorigo in news, physics, science.
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NB: This post is aimed at physicists.. However if you are not one, but you are really curious, you might find out that for once the annoying feeling of reading cryptic jargon is paid back by some real news!

I guess the most important message of the post you are about to read is: Do not check the arxiv today if you really cannot spend a couple of hours reading. Make it three. The  paper just released by CDF, titled “Study of multi-muon events produced in ppbar collisions at sqrt(s)=1.96 TeV” is guaranteed to have you fastened to the chair until you are done with its 70 pages.

The article reports on a very careful investigation produced by CDF, using Run II data collected by a trigger selecting events with two (or more) muons of low transverse energy. The study addresses two or three long-standing inconsistencies in measurements of bottom quark production and phenomenology at the Tevatron:

  • the cross section for b \bar b production appears in good agreement with next-to-leading order QCD predictions when b-quarks are tagged by a reconstruction of their decay vertex, while it is found to be significantly larger when the cross section is measured by identifying b-quarks through their semileptonic decay;
  • the invariant mass spectrum of pairs of leptons produced in sequential semileptonic decays (b \to l X \to l l' Y) is not well modeled by the simulation of b-flavored hadrons in CDF;
  • the value of the time-integrated mixing probability of b flavoured hadrons is measured at the Tevatron to be significantly larger than that measured by LEP experiments.

The source of these apparently unrelated inconsistencies is traced back by the study to a sample of events where muons are originated several centimeters away from the primary interaction point (the proton-antiproton collision vertex), which makes b-quark decay as implausible a source as any other Standard Model process, no better than the other backgrounds which the study shows to be insufficient explanation for the observed events: punch-through from pions and kaons, or secondary hadronic interactions in the detector material.

Once a large sample of such weird events are statistically isolated -better say evidenced- in the sample, a further anomaly is found in the number of additional muons contained in narrow cones around the original ones, something which cannot be easily explained with conventional physics. The paper discusses the characteristics of these events, without falling in the trap of putting together an exotic explanation. Instead, what is made clear in the paper is that those measurements quoted above -lepton-based cross sections and phenomenology of b-quarks studied in high-energy hadron collisions- are affected by the findings described in this paper.

Below I offer two plots extracted from the preprint. The first one shows the impact parameter distribution of muons in the events constituting the anomalous signal (black points), compared to the impact parameter of muons attributable to QCD sources (in red). The impact parameter resolution for these tracks is 2.5 times smaller than the bin size. One observes a abnormal tail of muons with very large impact parameter. I recall that the impact parameter, which is measured in the plane transverse to the beam direction, is the distance of closest approach of the backward extrapolation of the track to the primary interaction vertex. A impact parameter of one centimeter is huge, given that the typical decay length of a B meson is of the order of a pair of millimeters.

On the right you see an exponential fit to the impact parameter distribution of the trigger muons for the anomalous events, for events with just two (top) or more than two (bottom) muons inside two narrow cones around the trigger muons. The distribution agrees with the decay of a particle with a lifetime in the 20 picosecond range.

To quote the paper, the first lines of the Introduction offer a quite clear picture of the situation:

“This article presents the study of events, acquired with a dedicated dimuon trigger, that we are currently unable to fully explain with our understanding of the CDF II detector, trigger, and event reconstruction. We are continuing detailed studies with a longer timescale for completion, but we present here our current findings.

The conclusions are also clear, but I will leave them to those of you who want to read a paper which might, just might, constitute the first evidence of physics beyond the Standard Model, ever.

That said, if you have read this blog long enough, you know me for a tough sceptic. I of course would be simply delighted if the CDF signal of multi-muons really were a first evidence for new physics; but I have to play the devil’s advocate, and so one word of caution, make it five paragraphs, is mandatory. Of course, despite the evidence is pretty solid from a statistical standpoint, one must lean back and take a breath. We are discussing the possibility that something really spectacular has just lurked out of CDF data. Extraordinary claims require extraordinary evidence, and once statistical evidence is plain, one must delve with systematics. CDF did, and they have not found any significant source which might account for the effect. But investigations should and will continue.

Is CDF sure about the impossibility of explaining this effect away ? No, CDF does not exclude that possibility, although it is my opinion that the collaboration has reviewed the paper with more care and detail than most of the other papers it has published in its illustrious, 25-year-long life. That means nothing in terms of the likelihood that this result is indeed new physics. It just says we are as sure as we can be that we cannot presently explain it with known sources. Also worth mentioning is that CDF is a really disciplined collaboration, which has really been careful with their claims so far. And the present paper is no exception.

Is there a simple New Physics explanation of the observed effect ? No, as far as I understand no existing model of new physics predicted such a signature in advance, although one must acknowledge that a few ideas exist in the literature which might have a connection with the effect, if proven real. However, there is a paper discussing a similar signature, which probably benefitted from knowing the CDF result in advance from an internal source. I will leave this issue to another time and another place.

Can CDF find more evidence in the near future ? Yes, the analysis of electron events may shed more light on the matter, and although electrons are harder to isolate than muons when they have a low energy, the analysis will be carried out.

Can D0 find a similar signal ? Surely. D0 is a similar detector to CDF, and although their charged particle tracking is slightly inferior to CDF’s, their muon system is more extended, and their silicon detector is also at least as good as that of CDF (ok, even slightly better). The problem with D0, I think, is the time it will take to perform such a complicated analysis. One must not forget that before focusing on these anomalous events, CDF produced a lengthy investigation of the correlated b \bar b cross section, which is the back-bone of the multi-muon analysis, since it demonstrates the understanding of heavy flavors in low-transverse-momentum lepton samples in CDF when particles with large impact parameter are excluded. So, it may take a while to D0 to confirm or disprove the effect CDF is now publishing.

Does the signal hint at other anomalies in different analyses ? That, I am sorry to say, is anybody’s guess. If the multi-muon events are a signal of new physics, then I am sure there is something else to be found, somewhere. The problem is: what is that ? One might be tempted to speculate that data samples collected in past experiments could in principle contain a similar signature: charged tracks with very large impact parameter have been seldom studied at colliders, and tracking algorithms might have purposely discarded those tracks, or could be proven inefficient in their collection. For instance, CDF does collect, with its fantastic SVT trigger, events containing tracks showing a significant impact parameter. However, the efficiency with which the SVT collects those events, if studied as a function of impact parameter, dies out much too soon. Hell, nobody designs a detector aimed at collecting a new physics signature no theorists have thought about!

I imagine hordes of theoretical physicists canceling flights, conferences, and courses today, making room for some serious thinking in their agendas. Good luck!

UPDATE: see the interesting discussion developing at Peter Woit’s site, where he points out a paper by Arkani-Hamed and collaborators which appears quite extraordinarily to have foreseen the above signature of new physics, in a very timely fashion!

UPDATE: there are other bloggers who’ve discussed this. Lubos, Carl, Matti (happy birthday Matti). Others to be added soon…

UPDATE: other excellent, entertaining bloggers have added their own comments to the story: Jester, Chad, theorema egregium. In italian: Marco. In dutch: astroblogs.

UPDATE: John, a fellow collaborator in CDF and one very skilled physicist, explains the result at cosmic variance.

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1. Anonymous - October 31, 2008

Interesting. For the muons nearby the trigger muon: I didn’t see a plot of the chi^2 of the muon chamber hits to their COT/SVX track. Is there a plot of how that compares with isolated slow muons?

2. carlbrannen - October 31, 2008

This is the Centauro seen in cosmic ray experiments years ago. The best paper describing the Centauro signal is Are Centauros exotic signals of the QGP? by Ewa Gladysz-Dziadus which looks at them from the point of view of quark gluon plasma. Centauros were supposed to be explained a few years ago by the standard model. I can’t find the paper (by a Russian) at the moment.

The primary characteristic of Centauros are way too many leptons and not enough hadrons, or the reverse. There are other characteristics that are similar to the observation. And of course I’ve claimed that Centauros are evidence for a preon model for the elementary particles, but to get that one way or another we will have to wait for a lot more information on them.

3. ciro - October 31, 2008

Nice post !
I’m wondering if this result could be related to multi-muon bundles observed in exteded air showers, to my understanding a long-lasting problem of cosmic-ray physiscs.

4. tripitaka - October 31, 2008

very interesting news indeed!
…now all i have to do is wait for New Scientist to provide the full story (not).
Anyway, I’m heading off to check out Woit’s story.

5. dorigo - October 31, 2008

Hi Carl, Ciro,

not sure if these events have anything to do with centauros and cosmic ray phenomena, but, should they turn out to be new physics, many things could fit together. I remain sceptical though. Will educate myself with the link.

Tripi, I think indeed that most magazines will pick this story up. It just seems interesting: possible new physics, long-standing controversies, LHC dead in its tracks while the Tevatron rulez, etcetera.


6. jlm - October 31, 2008

Dear T.,

A rough estimate of the number of authors compared to the next most recent archive paper from CDF indicates that only 2/3 of the collaboration signed this paper. Any comment?

I find your remarks about whether this signal hints at anomalies in other measurements too cavalier. CDF has published a paper claiming that the superjets seen in RunI are no longer present. CDF measurements of the ttbar cross section using displaced vertices rely on determining the ratio of tagging efficiency in data and MC using a sample of non-isolated leptons (leptons in jets). Should we assume these measurements are not biased by a long-lived excess muon contribution? One infers from the present paper that since it only mentions how past analyses were biased by this ‘ghost’ contribution that CDF has concluded that present RunII analyses are unaffected. Can you confirm?

Wouldn’t ‘extraordinary evidence’ contain an analysis of electrons? Or an analysis of muons in a high-pt triggered sample?


7. Matti Pitkänen - October 31, 2008

Nothing new to me but two excellent birthday gifts at my birthday October 30;-).

TGD has predicted the existence of colored excitations of leptons explaining CDF anomaly already for fifteen years ago.

One of the basic predictions of TGD indeed is that leptons should have colored excitations. Already at seventeens a lot of evidence for colored electrons, or rather their pion like bound states, came from anomalous production of electron positron pairs in heavy ion collisions.
For some mysterious reason it was put under the carpet. I have tried to tell about this in blogs but in vain.

For year ago evidence for muo-pions came. Again it was forgotten although Lubos saw the trouble of ridiculing the experimenters.

CDF gives evidence for tau-pion. The lifetime predicted for charged tau-pion obtained by scaling the prediction for pion life-time is correct if one scales down the parameter x in the parameter f(pi)= xm(pi) characterizing pion coupling to axial current by factor .41. To my opinion the case is now closed.

The positron and electron positron cosmic ray anomalies can in turn be seen as evidence for M_89 copy of hadron physics.

See my blog.

Matti Pitkänen

8. Nicola - October 31, 2008

first love never betrays… very interesting job, CDF, very interesting!

9. Andrea Giammanco - October 31, 2008

> first evidence of physics beyond the Standard Model, ever.

You should specify “in a laboratory”, otherwise our fellow cosmologists will remind you that Dark Matter and Dark Energy are not explainable in the SM, and so constitute evidence of physics beyond it :)

I still have to read both this paper and Arkhani-Ahmed’s theoretical paper “predicting” (or better post-dicting) the effect.
But what about the following:
in some Susy variants, or other alternative models, the stau is a HSCP (heavy stable charged particle). HSCPs are easy to spot if their lifetime is long enough to traverse the detector (due to the high mass, you observe very high dE/dx and a time of flight incompatible with the speed of light), and if it is long enough to survive days or weeks or more, you can even spot them by their trapping in the cavern with subsequent decay (you observe a signal in the detector even without beam – of course then you must demonstrate they are not cosmics nor radioactivity, but the time dependence would help). But I’ve seen somewhere that O(10 ps) was quoted as lower bound on the lifetime, and this signal here has exactly the right order of magnitude :)

I hope somebody can comment on this: is this signal compatible with a stau production?

10. Not Even Wrong » Blog Archive » Discovery of a New Particle? - October 31, 2008

[...] There’s an excellent detailed posting about the paper from CDF’s own Tommaso Dorigo. If you’re interested in understanding [...]

11. Tony Smith - October 31, 2008

It is interesting to compare the treatment, by Fermilab and the USA physics community at large,
of Arkani-Hamed and Weiner
the treatment of Goldstein, Dalitz, and Sliwa some years ago (a situation that may have contributed to my current state of blacklisting/ostracism by the physics community).

Tony Smith

12. News from the CDF and PAMELA experiments « Theorema Egregium - October 31, 2008

[...] interesting, so I will link them here for my record. You are encouraged to read Woit’s and Dorigo’s posts on the first news and the Resonaances blog post on the second one. The technical [...]

13. Anonymous - October 31, 2008

BTW, the reason I asked the question above is with regard to a possibility of some fairly subtle crosstalk effects in the muon chambers. Such effects could potentially only show up (outside of the raw data) when the reconstruction attempts to match nearby COT tracks with hits along a road in the muon chambers.

BTW, as for so-called “centauro” cosmic ray events — those have an excess of hadrons, not leptons — this would be the exact opposite situation.

As Tommaso (and CDF, and the rest of the field) does (to its benefit), one should tend to look at experimental and detector effects before seeking new physics explanations.

14. carlbrannen - October 31, 2008

Tommaso, I should correct my note. The Centauro is an excess of hadrons. The excessive numbers of leptons and photons is called the anti-Centauro and is discussed in the same paper to a less degree. Anti-centauros are more difficult to detect using emulsion methods so there’s less evidence of them. I think they were seen at JACEE.

15. Very Naive - October 31, 2008

Charged pions decay to muons, although they live 10^4 ps. Is it possible that muon excess is due to anomalous pion production?

16. Haryo - October 31, 2008

Hi Tommaso,

Is there a public CDF webpage outlining the analysis, as well and listing the principal analyzers ?

17. dorigo - October 31, 2008

Ahem… Let me answer a few comments above here.

JLM: the superjet un-evidence analysis is un-conclusive. However, I do believe the superjets of Run I were a weird detector effect. I was a internal reviewer of the whole analyses by the authors of those papers (who also published the present one). I believe you know all of that.
As to what CDF analyses are affected, I think many, in principle. It will have to be assessed. However, I do not think the b-tagging efficiency is affected sizably. Usually leptons are required to have silicon hits.
An analysis of electrons is called for, and indeed, I do not think that we are at the level of extraordinary evidence, not nearly yet.
I am as sceptical as you are, with a “c” however, not a “k”.

Hi Matti,
I do not believe the case is closed. We will have to work very hard now to understand what is going on. Please understand: despite the fact that detector effects or known physics have not been found accounting for what is observed, it does not mean they cannot be the cause. So far, I believe that the extraordinary new physics these events point to is far less probable than a less exotic explanation in terms of some misunderstanding of detector or backgrounds.

Hi Andrea,

the signal, as far as I understand, is compatible with a chain cascade decay of many tau leptons, rather than a single stau. We will see however. There should be a paper interpreting the result out soon.

Tony, there are similarities, but it is a different matter. Sliwa was in CDF back then (as he is now BTW), here the pheno papers contain no CDF author names.

Anon, the signal of multiple muons arises by associating different COT tracks to different muon candidates. Yes, a cross-talk between different muon chambers could make fake muons appear… Why shoud we see it only when the muon has a large impact parameter ????

Carl, thanks for the note. Yes, the centauro events are a splashout of hadronic energy in the detector, with no jet structure.

Hi Very,
no, pion decay is not a possible source. An anomalous pion… Well, then, who knows ? Maybe.

Hi Haryo,
no public page yet. Sorry…

Cheers all,

18. Tony Smith - October 31, 2008

Anonymous mentioned “crosstalk effects in the muon chambers”.

Could Anonymous and/or Tommaso here give some more details about such crosstalk effects?

Tony Smith

19. dorigo - October 31, 2008

Hi Tony,
muon chambers have an electronics readout built on the front-end, with preamplifiers. In principle those can chat with each other. There is no reason they should do it only in high-impact parameter muon stubs.


20. Anonymous - October 31, 2008

> Why shoud we see it only when the muon has a large impact
> parameter ????

don’t know — perhaps a reconstruction software effect? good question, of course.

> Could Anonymous and/or Tommaso here give some more details > about such crosstalk effects?

Anonymous doesn’t have specifics in this situation, because Anonymous is not on CDF. But in general, crosstalk is a fairly common effect in electronics (due to cross-capacitance — it in fact is what limits the bus speed in computers and is, for example, why CPUs now have a backside memory cache) and also occasionally due to actual particle/nuclear effects (scattering, delta rays, spallation, other nuclear interactions). It’s always one (of many) places to look when things like this occur.

21. john - October 31, 2008

It will be interesting to see how this turns out, but I’ll leave it to those more closely involved to evaluate all of the new physics vs old physics vs complicated analysis issues.

However, looking at the data brings up some issues I’ve been discussing with students lately; subtleties of fitting data, in particular treating error bars for low statistics data. Since issues of this kind (fitting tails with low statistics, looking for peaks on large backgrounds, etc…) are much more common in this kind of experiment, I was hoping there might be some nice, clear writeups dealing with such issues that would be appropriate for introducing students to this kind of issue. I’m hoping you or one of your readers can point me to something that’s both clear and hands-on.

22. Haelfix - November 1, 2008

It would be interesting to see a detailed analysis of the predictions of the Superunified dark model vs whats observed. At first glance I don’t see why they would see such a large excess with the integrated luminosity CDF has utilized.

It would make much more sense if the data had been from an LHC run. I mean the excess is really unusually large.

23. changcho - November 1, 2008

Well, this is great news for the CDF team, now with the LHC out of commission for a while the paper came out in the right window of time. Hope it’s real…

24. Tom Wright - November 1, 2008

JLM, you raise an interesting point about the b-tag efficiency calibration. The muon itself is not required to have any hits from the silicon detector attached or any particular impact parameter, so it could conceivably be from this anomalous population. However, we require a displaced vertex tag in a jet opposite the muon, which should enhance the b-bbar component relative to the anomalous piece. The vertex tagger applies a maximum impact parameter cut of 1.5mm on tracks and prefers tracks with silicon hits on the inner layers, so it would rarely ever try to make a vertex out of these anomalous muons. I think it is unlikely to have an effect but it’s something for the b-tag group to check out, thanks for pointing it out.

25. Matti Pitkänen - November 1, 2008

Dear Tommaso,

I should have said: I believe that the case is closed! It is is easy to forget “I believe”s when the conformation of the prediction of a model finally comes after one and half decade of patient waiting.

Why I believe that the case is closed is that this new anomaly fits nicely to a larger pattern: entire sequence of anomalies – one for each lepton generation – is explained by the mere assumption that leptons have colored excitations as indeed predicted by TGD whose basic structure is fixed uniquely by the requirement that it geometrizes standard model symmetries.

Concerning anti-Centauros: they might relate to the jets of colored leptons since a collision of charged particles with extremely high energies creates strong non-orthogonal electric and magnetic fields able to generate the leptopion coherent state. There are also other explanations in TGD framework.

Matti Pitkänen

26. mdelma - November 1, 2008

Ciao Tommaso,

I just finished to read the paper yesterday night. Among all, one things puzzles me: the very low correlation between impact parameter of muons in the same cone (read: in the muon “jet”), I don’t know, it doesn’t sound right, but I might be missing something… Would this be compatible with the a chain cascade decay of many tau leptons?

27. Matti Pitkänen - November 1, 2008

Still a comment about leptohadron hypothesis.

The surprising finding of PAMELA is that positron fraction (the ratio of flux of positrons to the sum of electron and positron fluxes) increases above 10 GeV. If positrons emerge from secondary production during the propagation of cosmic ray-nuclei, this ratio should decrease if only standard physics is be involved with the collisions. This is taken as evidence for the production of electron-positron pairs, possibly in the decays of dark matter particles.

Leptohadron hypothesis predicts that in high energy collisions of charged nuclei with charged particles of matter it is possible to produce also charged electro-pions, which decay to electrons or positrons depending on their charge and produce the electronic counterparts of the jets discovered in CDF. This proposal – and more generally leptohadron hypothesis – could be tested by trying to find whether also electronic jets can be found in proton-proton collisions. They should be present at considerably lower energies than muon jets.

The simple-minded guess is that for proton-proton collisions the center of mass energy at which the jet formation begins to make itself visible is in constant ratio to the mass of charged lepton. From CDF data this ratio is around sqrt(s)/m(τ) about 10^3. For electropions the threshold energy would be around .5 GeV and for muo-pions around 100 GeV. In fact, I found that I have told in Recent Status of Leptohadron Hypothesis years ago about production of anomalous electron-positron pairs in hadronic reactions [1,2,3,4] as evidence for lepto-hadron hypothesis.

[1] T. Akesson et al (1987), Phys. Lett. B192,
463, T. Akesson et al (1987), Phys. Rev. D36,

[2] A.T. Goshaw et al (1979), Phys. Rev. Lett. 43,

[3] P.V. Chliapnikov et al (1984), Phys. Lett. B
141, 276.

[4]S. Barshay (1992) , Mod. Phys. Lett. A, Vol 7, No
20, p. 1843.

28. Fermilab heeft wellicht ‘iets’ ontdekt en Astroblogs - November 1, 2008

[...] });Noot:Zie bijvoorbeeld Tommaso Dorigo, Peter Woit, Lubos en Carl. [↩]Eén commentator zegt dat het wellicht om een Centauro gaat. [...]

29. Tony Smith - November 1, 2008

Peter Woit said on his blog:
“… the CDF web-server was seriously misconfigured, allowing directory listings and public access …[by]… Google searches on relevant terms … to a wide array of their work materials …[including, with respect to CDF multimuons]… a summary of CDF’s internal review of drafts of PRL and PRD papers on the subject …[and]… the PRL draft … these documents were from early July [2008]… the PRL draft contained tentative material interpreting the data in terms of new physics, the sort of thing the released paper avoids.
One thing I [Peter Woit] can say is that it is very impressive to see the amount of effort and very serious scientific work behind a review of this kind …[To]… make this kind of thing public … actually would be a wonderful example for the public of how science is done ….”.

Is there any serious constituency at Fermilab or CERN that would like to allow public access to such work material ?

It seems to me that it would be a good thing for lab collaborations (Fermilab, CERN, et al) to do:
As Peter says, public transparency would show “… the public … how science is done …”,
and that should increase both
public confidence in the scientific processes at the labs and
public understanding of how science really works.
That should probably lead to a more sympathetic public view of inevitable glitches,
both theoretical/analytical (example – Rubbia’s 40 GeV T-quark)
and experimental (example – recent helium release at CERN).

Further, it would allow non-collaboration physicists to have equal early access to data and ideas, which (since here I am only discussing publicly funded laboratories doing no military-classified research),
although it might increase the amount of noise in physics discussions,
might well produce some good physics
that might have been delayed (in the case of ideas from physicists outside the collaborations and without “inside sources” to feed them stuff that is now non-public)
or suppressed (in the case of ideas from physicists inside the collaborations) by requirements of consensus approval for public release.

For example – What if the Challenger Commission had prohibited Feynman from doing his public O-ring in ice water demonstration,
and/or had banned his Minority Report from publication and ordered him (on penalty of not only him losing his status as Commission member, but also of Caltech being banned from participating on any Commission) to keep his mouth shut about his ideas ?

Tony Smith

PS – Peter said, of the CDF web-server misconfiguration, that now “… they have fixed it …”.

30. dorigo - November 1, 2008

#20: no, a reconstruction software bias toward high-IP tracks is very much off the board. Those tracks have been scanned individually in high-muon-multiplicity events, and no particular effect has been noticed.

#21: yes, I have dealt with issues such as those you mention so many times I would be embarassed if I had to offer a single link to one of my posts. Just search stuff in google, like “statistics site:dorigo.wordpress.com”, or “fit site:dorigo.wordpress.com”, or things alike. Of course, if you have something particular to propose as a topic for a next post I will be obliged to offer one example.

#22: haelfix, yes the effect is large, it seems to imply we are dealing with a very common phenomenon. That is one of the reasons why most of us still think at QCD fake muons of some kind as the most likely source of the anomalous muons.

#23: changcho, I do hope this is real. Since I like to bet, I would estimate odds that this is new physics at 1%. One percent is HUGE!
But it still is one percent :)

#24: Hi Tom, thanks for the note, I in fact did not remember well whether we apply SVX requirements on the lepton in the tagging efficiency method.

#25: Hi Matti, Yes, it is important to specify that what one writes is just a personal belief. Otherwise rather than scientists we look like magicians, and that is BAD.

#26: Hi Marco, yes, the non-correlation of impact parameters on one side rejects several background hypotheses, on the other discards several new physics interpretations. I think you need to wait a paper by the authors, which will come out on Monday, about how to intepret the events.

#27: be careful Matti, the Tevatron has a variable sqrt(s). Parton distribution functions force sqrt(shat) to be a exponentially falling function. What that means is that low-energy interactions are always most favored. Only one interaction in a billion has a sqrt(shat) of 1 TeV.

#29: Tony, forget it. Large collaborations have many reasons to keep their internal affairs internal. Whether that is the best thing for science or what, I personally do not know. I am certainly in favor of publishing controversial results rather than keeping them in the drawer for years, but as for distributing internal meeting slides or notes… Well, I am not so sure it is a good idea. Maybe it is, but we are not yet prepared to it…

Cheers all,

31. Shantanu - November 2, 2008

Tomasso, you said :

“The conclusions are also clear, but I will leave them to those of you who want to read a paper which might, just might, constitute the first evidence of physics beyond the Standard Model, ever.”

I disagree with this. You forgot the evidence for neutrino mass which
happened 10 years earlier.

32. Andrea Giammanco - November 2, 2008

I disagree with Shantanu. Non-zero neutrino masses can be accounted for in the SM vey straightforwardly.
You can argue that their smallness is unnatural and this can be a hint of new physics (e.g., m_nu linked to M_gut through see-saw) but:
1 – the entire spectrum of known particles is completely unnatural, e.g. there is no SM explanation for the top-bottom mass splitting (why so different from the charm-strange?), so one could argue as well that *all* masses are evidence for physics beyond the SM
2 – if we stick to the idea that neutrino masses are too unnatural even in a quite unnatural overall spectrum, then the evidence is not to be dated to their first non-zero measurement, but to the plenty of experiments, during year, which were able to set upper limits tight enough to make it apparent that neutrino masses were so unnatural
3 – if you argue that an exactly 0 mass would have been more natural than a very small mass, because at least it would have implied a symmetry to protect it (and so it would not be a random number), I will argue the this symmetry would not be SM either, so the actual measurement of a small non-zero mass did not change the status of the SM-ness of the neutrinos.

33. Matti Pitkänen - November 2, 2008

Dear Tommaso,

thank you for a critical argument. It inspired me to develop a detailed argument for two situations corresponding to the cases when the field E and B of colliding proton and antiproton (quark and antiquark) are responsible for production.

The argument gave a justification for my guess if its em fields of proton and antiproton which are responsible for the production plus an argument suggesting that Planck constant increasing phase transition must take place in the process so that leptopions would be dark in TGD sense. I reached earlier the same conclusion in the case of electro-pion production in the collision of heavy ions since otherwise cross section for production remains somewhat too small.


34. Arun - November 2, 2008

Tommaso gives the probability of this being new physics at 1% and is tremendously excited.

To give some perspective, fivethirtyeight.com gives McCain a 3.8% chance of winning the US presidential elections; and McCain supporters are tremendously depressed. :)


Superdark matter is a top-down construction of what this new phenomenon might be. Isn’t it better to do a bottoms-up reconstruction? Assuming a new particle, get a few of its properties before trying to embed it in a model?

35. Shantanu - November 2, 2008

Andrea, first time I am reading that a non-zero neutrino mass
does NOT constitute evidence for beyond standard model physics.
If you look at the press releases following discovering of neutrino
oscillations , all of them are of the consensus
that this is evidence for physics beyond standard model.
Also the standard model as presented in textbooks assumes
neutrinos have zero mass. Can you (or someone else) provide some references which explains how neutrino mass can be accomodated in standard model?

36. Guess Who - November 2, 2008

Shantanu, just Google up “MNS matrix”. It’s just the lepton equivalent of the Cabibbo-KM matrix for quarks. Old textbooks used to assume neutrino masses = 0, which made the MNS matrix trivial. But there’s nothing really new in it.

37. dorigo - November 2, 2008

I also disagree with Shantanu, and Andrea explained very well what I also think.

Arun, I want the SM to go down, Obama to go up…. But in any case, whomever gets elected, will not change our perspective so much as a whole sector of physics disclosing before our eyes.. So yes, it excites much, much more even if chances are slim.

Hi Matti,
I am unable to understand if your model fits in with the present observation, but I will keep an eye on it. Do not expect me to understand much though ;-)

Cheers all,

38. CDF Ghost Muons | Cosmic Variance - November 2, 2008

[...] you want more details, there is a very nice and much more physicist-oriented post by Tommaso Dorigo available at his [...]

39. Alejandro Rivero - November 2, 2008

We have already told about another mistery in the 1-6GeV energy range: the stability of the B and Ypsilon mesons is greater than the stability expected by the naive rules (respectively the “spectator quark” rule and the “mistery line” of http://dorigo.wordpress.com/2006/09/14/a-mistery-behind-the-z-width/ )

(for single quark decay, see http://www.physicsforums.com/showthread.php?p=1482998 )

40. Andrea Giammanco - November 2, 2008

Shantanu, the straightforward way to account for neutrino masses in the SM is just to allow them to have a Dirac mass term in the lagrangian, i.e. be like all other fermions in the SM.
But the neutrino masses are so small (all the three of them), that many people have thought that it could be more than just a coincidence.
One way to make small masses is to allow a Majorana mass term and let the see-saw mechanism intervene:
By putting in the lagrangian a “reasonable” Dirac mass (of the same order of the charged leptons) and a Majorana mass of the order of the Grand Unification scale, one gets more or less the right order of magnitude for the physically measured neutrino masses.
This argument is taken seriously by many, as a hint of Grand Unification, but it is certainly not a proof.
Anyway, whatever you do there is something “innatural” about neutrino masses. The options have historically been:
1) neutrinos have mass 0 (exactly); why? (I.e., which unknown symmetry of nature acts on neutrinos and not on all other fermions?). This has been ruled out 10 years ago.
2) neutrinos have a Majorana mass of the order of magnitude of the GUT scale; why only neutrinos?
3) neutrino masses are small because they are small (i.e. they only have a Dirac mass term, and by chance this mass is so much smaller than the charged leptons); this is the dumbest hypothesis, but not so much dumber than answering “why is the top mass so much heavier than all other quarks?”

There are several ad-hoc solutions, on the market, also for the special mass of the top quark (models in which the top quark has a special role, and many of them are not ruled out yet).
But I hope that one day there will be a working theory predicting the whole observed mass spectrum in one go, without separate fixes for the neutrino sector and the heavy quark sector.

41. Shantanu - November 2, 2008

Hi, Can someone provide me references where neutrino mass
is included/incorporated in the Standard model Lagrangian? google is not always reliable. I have a copy of
Quigg’s book with me(2nd edition) and in the sixth chapter (which is on standard model) , neutrino mass is assumed to be 0.

also assuming you people are right (though I would like to read the literature), does that mean neutrino results have been oversold
(as evidence for physics beyond standard model)?

42. Big Vlad - November 2, 2008


In the standard model there is no reason why neutrinos cannot acquire mass in the same way that other fermions do – i.e through Yukawa interactions with the Higgs. Of course, the corresponding Yukawa coupling constants would be tiny because the nu masses are so small.

43. Guess Who - November 2, 2008

The Particle Data Group reviews of the Standard Model


include a chapter (number 13) on “NEUTRINO MASS, MIXING, AND FLAVOR CHANGE”:


The standard NMS references are the first ones in that chapter (old stuff, from 1962 and 1967).

Yes, there was some excessive hype about the significance of finite neutrino masses ten years ago. But their smallness, and the difference in structure between MNS and Cabibbo-KM matrix may be a hint of… something. ;)

44. Alejandro Rivero - November 2, 2008

Hmm from my own reasoning in #39, one could expect that this object is the real main decay product of the Upsilon. Could it be?

45. Just Studying - November 3, 2008

I apologize if this is a silly question, but could an undetected flux of naturally occurring neutrinos suppress the decay event?

Also, I wasn’t sure if this was in the report, but did they look to see if the jet varied over time?

46. Matti Pitkänen - November 3, 2008

Dear Tommaso,

the model without further calculations explains the following observations.

a) Jets results by the same mechanism as in QCD from decays of bound states of tau-baryons and tau-mesons. I have considered in detail the decay mechanism leading from colored excitations to ground state here.

b) Muons dominate if the masses of tau and tau_c (nu and nu_c) are near to each other because there is very little phase space for tau final states. The near equality of the masses is motivated by the fact that this is true for e_c and mu_c. In the case of electron the small electron mass reduces the phase space. In the case of neutrino the equality is not checked: it would predict that charge electropion has mass nearly equal to that of electron. I have very probably discussed this point in the above link: this would of course relate to the anomalous production of electron positron pairs discovered already at seventies but for some reason forgotten since then.

c) The numbers of anomalous muons with opposite charges are same since neutral taupion initiates the jets.

d) One can also calculate the life times of neutral and charged tau-pions just by putting to the standard formula for lifetimes of ordinary pions appropriate masses. Charged pion decays weakly and everything is calculable using PCAC hypothesis (pion field proportional to axial current), neutral pion decays weak two photon channel dominantly and anomaly considerations fix the Lagrangian to product of tau-pion field and E.B with a coefficient involving only axial coupling f(pi)= xm(pi), fine structure constant, m(pi)… The prediction is correct is x is scaled down from that for ordinary pion by a factor of .4. I would not like to sound like a teacher but add this result should really wake up everyone in the audience.

Also the total rate for virtual leptopion production is calculable using the product of leptopion field and instanton action E.B. This requires a model for the collision. The simplest thing to do is to start with is free collision parameterized by impact parameter and velocity and integration of differential cross section over impact parameter values up to infrared cutoff, which must be posed in order to have a finite result. This was done in case of lepto-electron production using classical model for orbits of ions and resulting E and B. In the case of electropion atomic size was the first guess for the cutoff. Now tau-pion Compton length is the first guess. One can estimate from this the rate for the production of leptopions and since this is the rate determining step, the total rate for production of anomalous muons via jet mechanism.


47. Arun - November 3, 2008

It seems the consensus is that neutrino masses are within the standard model.

The general headings are as follows:

I. Theoretical and Mathematical Physics
Mathematics for Physics Applications, Quantum Mechanics, Quantum Field Theory, Gravity, Supersymmetry and Supergravity, String Theory, Condensed Matter Physics.

II. Elementary Particle Physics – Standard Model
General Aspects of Elementary Particles, Quantum Electrodynamics, Strong Interactions, Weak Interactions, CP Violation and Flavor-Changing Weak Interactions, Neutrino Masses and Mixings.

III. Elementary Particle Physics – Beyond the Standard Model
Higgs Boson Physics, Technicolor and Composite Higgs, Supersymmetry, Models with Extra Space Dimensions, Exotic Particles, Grand Unification, Experiments in Physics Beyond the Standard Model.


48. 74. Nima and CDF anomaly - November 3, 2008

[...] (see for example discussions by Lubos, Tommaso Dorigo who is the member of the CDF team, and Peter Woit) is into the CDF anomaly during last couple of [...]

49. Nima Arkani-Hamed - November 3, 2008


As most of my friends and colleagues know, I have a very dim view of
the physics blogosphere, and avoid interacting with it. However, your
statements about me and my collaborators in connection with the recent CDF anomaly quite clearly crossed a line, and I feel compelled to respond. In doing so I am adopting an attitude Howard Georgi once described when dealing with non-perturbative QCD effects in heavy quark effective theory: once I am finished dealing with the brown muck, I will wash my hands.

It was stimulating to see the CDF paper. However, this is an extremely challenging analysis, and many further cross-checks will have to be done to take it as a serious indication for physics beyond the standard model. We are all well aware that particle physics anomalies have come and gone in the past two decades, in analyses that are less complicated than this one; of course the collaboration made no claim to have discovered new physics. Keeping this in mind, let me first make comments on some physics I have been involved with, and end with some comments on sociology.

I have been working recently with Doug Finkbeiner,Tracy Slatyer and Neal Weiner on a theory for dark matter motivated by a growing number of anomalies in astrophysics, most recently PAMELA/ATIC.
This work is a direct continuation of (in my view) beautiful earlier work pioneered by Neal, Doug and Dave Tucker-Smith, who have collectively pushed it for many years. In fact, Neal, Doug and others previously talked about GeV scalars decaying to leptons in the context of “exciting” dark matter, to explain the INTEGRAL signal, as well as the HEAT excess predecessor to PAMELA. So the idea of GeVish mass particles decaying to leptons, motivated by Dark Matter anomalies, goes back to Feb 2007–Feb 2008. See e.g. astro-ph/0702587 and especially arXiv:0802.2922.

What we did in our four author paper was to show that all these strands fit together into a simple unified picture that also makes very good particle physics sense. The idea can be summarized in one sentence: Dark Matter is charged under a non-Abelian gauge symmetry broken at the GeV scale. We pointed out two additional major motivations for the GeV scale–first, the new vectors with this mass naturally “Sommerfeld enhance” the annihilation cross section as appears necessary to explain the PAMELA/ATIC signals from DM
annihilation; second, the broken gauge symmetry at the GeV scale radiatively induces splittings between the different states in the DM multiplet at the \sim MeV scale, which is precisely what is needed in “exciting” and “inelastic” DM explanations of the INTEGRAL and DAMA signals. All of these phenomena, scattered over energy scales ranging from a TeV to an MeV, are essentially a consequence of the single sentence I used to describe our picture above. We find this compelling.

Since the GeV gauge sector is non-Abelian, there are a number of
states, minimally including vectors and higgses, all GeVish in mass.
One thing that happens when at least some of these GeV particles are vectors is that they can easily talk to the Standard Model, via kinetic mixing with the photon. The mixing is naturally small, so directly producing this particle is challenging–though people have
talked about doing it at low-energy e+ e- machines (B-factories,
DAPHNE, BESS). Neal and I considered the simplest marriage of our DM picture with low-energy SUSY, which further naturally generates the GeV dark gauge symmetry breaking scale. We also
pointed out that in this set-up, one could produce particles in this new GeV sector much more copiously, not directly, but indirectly through SUSY production: every SUSY event will end with MSSM LSP’s which then decay into the true LSP in the dark sector; essentially all of these will also be accompanied by some of the GeVish particles that re-decay back into SM leptons. One would expect a cascade of decays in the GeV sector given the multiplicity of states, and thus the aptly named “lepton jets”. We discussed displaced vertices as a possibility, though they are not guaranteed. So, seeing “lepton jets” as an O(1) fraction of SUSY signals is what we talked about as the smoking gun of our model at the LHC. It would indeed be an amazing signal, which is why we were and continue to be very excited about it!

Now, even if the CDF anomalies are an indication of new physics–which I think in all of our views is _very_ far from obvious– it can not be due to the signal Neal and I talked about, arising from SUSY cascade decays. The rate of the CDF anomaly is absolutely
enormous–you are talking about 70,000 “ghost” events! If there is a connection to our model at all, it would likely have to be through direct production of the GeV sector particles, that still cascade decay in the dark sector and produce the lepton jets. As I mentioned there are limits one can put on this from e+ e- data, and a number of us had been wondering what could be done at hadron colliders, but at least my instinct was that the rates wouldn’t be high enough and it would be far too messy and difficult to extract a signal. We were planning on thinking about this in more detail soon, but the exploration of the consequences of our model is very new, and for now most of us have been focusing on getting out the important predictions on the DM side for GLAST/Fermi, as well as fleshing out the big O(1) LHC predictions. Obviously, stimulated by the CDF result, studying the question of direct production at the Tevatron is much higher on our list of priorities, and we are looking at it now to see if it can even be in the right ballpark. But to re-iterate: even if the CDF anomaly is new physics, and even if it is connected to our model, (and needless to say these are two very big “ifs”), it would be a wonderful surprise to me since I had expected probing direct production of the GeV sector to be incredibly difficult at a hadron collider.

So much for the physics. Turning to the sociology: you publicly suggested that we had gotten wind of the CDF experimental result ahead of time, and casually wrote this paper pointing out the signal before the experimental result was published. Your only evidence is that we made a surprising prediction of a signal experimentalists hadn’t thought of before and put it out before the experimental
results were made public–Gasp! Shocking! Scandalous! Never happened in the history of physics! Not contained in the definition of the word “pre”diction! This was a hilariously preposterous accusation;
however it stopped being funny when you went further and all but
called Neal a liar when he stated unequivocally that we had no advance knowledge of the CDF result–this is outrageous. As Neal said, we had no knowledge about the experimental result ahead of time _at all_. We didn’t even talk about the Tevatron in our paper! And as I said above, even if this anomaly is real and even if it is related to our model, it can not be literally the signal we talked about. Also, the thought that we could somehow cook up a model motivated by explaining dark matter anomalies as a cover to explain rumored events at CDF is absurd–ask any theorist friends you may have whether this is feasible and you will get a good chuckle out of them. You think this signal “came out of the blue”, but if you have been following any of the developments in BSM collider physics in the past couple of years you will realize that signals involving high particle multiplicities with displaced vertices have been discussed for quite a while–check out the repeated use of the phrase “hidden valley” in my paper with Neal for references to work by Strassler, Zurek et. al. Our contribution is that a rather specific version of such a picture–with the GeV mass scale and coupling to the SM through kinetic mixing with the photon–is naturally singled out by the new picture of dark matter we put forward with Doug and Tracy, giving a potentially exciting connection between what we are now seeing in the sky and what we might see at colliders. As it happens this type of hidden valley model had not been discussed in the literature, so we happily pointed out some of their possibly dramatic LHC consequences. Perhaps if you had bothered to even superficially read our papers and think about the physics, it wouldn’t seem so “out of the blue” to you, and you would understand that these light GeV particles decaying to leptons are a necessary feature of our model of Dark Matter, whether CDF saw any hints for them or not.

I find your cynicism remarkable. We are entering what promises to be a golden era of amazing experiments in high-energy physics, astrophysics and cosmology, which may very well lead to profound advances in our understanding of Nature at a fundamental level. All of us–experimentalists and theorists alike–are fantastically excited about this and are doing everything we can to give it the best chance of happening. And at least most of us don’t think of physics as a soap opera rife with rumor and innuendo, or spend the precious time we have cynically tossing around completely baseless and deeply offensive accusations.

Speaking of precious time, I’m sure you’ll agree that there is more critical physics to do than there are hours in the day to do it,
and I for one would like to get back to work.

Nima Arkani-Hamed

50. dorigo - November 3, 2008

Dear Nima,

thank you for taking the time to explain more in detail what was the creative process behind the two papers you recently published. If you read my comment on Peter’s blog, you know I did ask for something like what you wrote above: an explanation of how you came to consider the striking signature we are discussing about.

If I insulted you or your colleagues with my remark, then please accept my apology, and forward these to them. I am a sceptic not only with respect to SUSY (which may be excused, since I am in good company), but also with respect of the CDF result itself. And I found it really a remarkable coincidence, to avoid putting new words out which may be found aggressive, that no more than three weeks before the CDF result is aired, you come up with lepton jets, with long lifetime, and with small invariant mass. Of course, that is not a copyrighted signature, so I am the one at fault – I am speculating. But indeed, I was not the only one who found this coincidence fishy. Many of my colleagues in CDF did, and so did others outside.

So, to summarize: I am pleased that you chose to come down to this blog to explain what caused you to discuss that signature. I will need time to digest what you wrote, because I am basically an ignorant. In earnest, I have to say I am still sceptical that there were no influences in your creative process. But I guess that is ok. The material is there for anybody to read and make their own opinion, and your text above will help creating those opinions.

Keep up with the good work,

51. Interpretation of multi-muons! « A Quantum Diaries Survivor - November 3, 2008

[...] paper was born as part of the other document (see the story in the post below), but was extracted from it and published separately since this was the best way to proceed [...]

52. Nima Arkani-Hamed’s letter on multi-muons - and my reply « A Quantum Diaries Survivor - November 3, 2008

[...] jets, produced by particles with long lifetime – a signature strikingly similar to the one CDF published a few days [...]

53. Arun - November 3, 2008

Hi Tommaso, sorry to see you set to the level of brown muck.

54. Pavel Murat - November 3, 2008

There are few important details the paper, Tommaso refers to, doesn’t say. Without these details the picture is very incomplete.

a) muon identification: “muons” discussed in the paper are dominated by the fake background – CDF internal review of the paper showed this very clearly

b) tails in the impact parameter distributions of the “muons” (Tommaso has them in the original post): the tails are consistent with being due to the interactions of the particles in the CDF detector material and Ks/Lambda decays. Same tails are present in the distributions for _any_ subset of the tracks and are well described by the CDF detector simulation

c) multiplicity distributions for observed “muons” are consistent with their source being hadronic punchthrough. In brief, the effect is due to hadronic jets punching through the calorimeter and producing hits in the muon chambers after which ‘muons’ are reconstructed as a random associations of hits with one of the tracks inside a jet. Given that there simultaneously are many tracks and many muon hits in the same region of phase space (directioin), probability of finding several track-hits matches simultaneously is high.

In summary, this paper doesn’t really report any new physics result but one more time proves that when one is not using identification cuts, his analysis sample is dominated by difficult to quantify background (in this particular case – hadronic punchthrough, secondary interactions in the detector material and decays in flight ).

Finally, I have to mention, that about 1/3 of the collaboration took their names from the author list of this paper.

best regards, Pasha

55. dorigo - November 3, 2008

Hi Alejandro,

thanks for pointing out the inconsistency of lifetimes of weak-decaying objects. It is something to watch out.

Shantanu, well… At the risk of pissing off 30% of my colleagues: yes. I think neutrino mass is an oversold topic. We have always made them zero, and simplified our theoretical model, but the neutrino mass does not add anything spectacular.

Alejandro, I don’t think so, because if the Y mainly decays to these unknown final states, then its cross section is way too high.

Just Studying, neutrino fluxes happen during supernova events, but they are just bursts – these data from CDF come from years of data taking. Also, neutrinos have zero probability of giving an interaction in CDF in coincidence with a bunch crossing, even if you imagine apocalyptic fluxes.

Matti, you have to excuse me if I am unable to follow your line of reasoning. I sincerely am sorry because I am guilty of not studying what you are putting forth, but unfortunately I feel unqualified, and so this becomes a lower-priority obligation – However, I am sure there are readers here that will be interested in knowing more of what you propose.

Arun, brown muck may sound bad, but I guess that’s the way many will call the next US president. So I feel no obligation to feel outraged by the attempted insult. Go Obama!

Hello Pasha,

(To put things in perspective: Pasha is a colleague in CDF, and I personally think he is a very skilled physicist. However, he was one very strong opposer of Giromini’s paper, and he produced an internal document which claimed to have “explained away” the anomaly. Since his proof was found to be at least not totally convincing, the paper received a green light from the spokespersons.)

If you want my opinion Pasha, I agree with you that it looks like this is some background due to relaxing too much the identification cuts of muons. However, you cannot deny that the analysis is bold and that the background it focused on is something we, in CDF, have not understood yet. So I believe the paper is worth publishing. I think you did not sign it, and I think this is a mistake.

Cheers all,

56. CDF , - - November 3, 2008

[...] CDF. , , , [...]

57. Pavel Murat - November 3, 2008

[aiming on professional audience]

my point is that there is enough features of the analyzed data
sample known to the authors which should’ve been described in the paper (it is a PRD, no space limits) to make it possible for the qualified readers to make their own judgement in an unbiased way.

In addition to the what I briefly mentioned above, HEP physicists reading this blog also may be interested to know that the new, exciting and unexplained physics effect was ‘observed’ using data ntuples compressed for B-physics analyses and not containing the calorimeter information. Without this information it was certainly impossible to see that the ‘interesting events’ were QCD dijets punching through the calorimeter and firing the dimuon trigger…

This sure is ‘bold’, I agree, just …mmm… not professional.

-regards, Pasha [murat-at-fnal-dot-gov]

58. dorigo - November 3, 2008

Pasha. as you certainly know, disclosing internal information about CDF analyses is reproached by our collaboration. So please avoid doing this.

In any case, things are not as you state. There was a six-month review of the work, done by a few of our best men in CDF, and they reproduced the results independently, looked at all the information they deemed important, and concluded there was no hint that the mundane interpretation you discussed above was likely.

I am sorry to say, Pasha, that in this story you end up the sorry loser, regardless of what turns out to be the truth concerning the multi-muon events. I say I am sorry because I am. You spent a lot of time reviewing the analysis, but could not convince your peer, not even those who would have loved to be convinced, that the muons were background. I think you had good ideas though, and with some more professionality you could have followed them without trying to adapt them to your conclusions.

I think you are probably right about the physics, but you made a bad service to CDF with your badly cooked counter-analysis.


59. Ray Culbertson - November 4, 2008

Contrary to being a “sorry loser”, I, and others, believe we owe many thanks to Pasha for taking a proper skeptical scientific approach to this analysis. He has worked directly to understand this data while virtually everyone else has simply chatted about the comments. He has made a good case for for being very suspicious of correlated hadronic punchthrough. In the end the paper went out (I could discuss that process for hours) but it was not because Pasha was a “loser”.

60. Top Posts « WordPress.com - November 4, 2008

[...] CDF publishes multi-muons!!!! NB: This post is aimed at physicists.. However if you are not one, but you are really curious, you might find out that [...] [...]

61. Pavel Murat - November 4, 2008

hi Ray, [good to see you here!]

important is that in his last posting on this thread Tommaso admitted: “I think you are probably right about the physics”. So we seem to agree on that – and this is what, I think, ultimately matters!

-regards, Pasha [murat-at-fnal-dot-gov]

62. dorigo - November 4, 2008

Hi Pasha,

yes, that is what matters to me too. And in fact, I knew you would not feel offended by my remark about the ineffectiveness of your investigations. I do not, however, think Ray is fair when he says other people chatted while you worked. Ray, you know that is really untrue. What to make of the work of Doug, Kevin, Mark (just to name a few) ?


63. chris - November 4, 2008

Dear Tomaso,

i have talked to an experimental colleague for whom i have very high regards and he essentially told me that you can get all kinds of low energy high multiplicity signatures easily when you are off ever so slightly with the b-quark mass in the event generators. now i am perfectly aware that your team is probably full of pythia&co experts that know this inside out, but i still would be very interested in your take on it. you know the usual problems with the b mass, i.e. whether you take pole or resonance mass etc.

64. dorigo - November 4, 2008

Hi Chris,

the striking thing of the CDF signal is not the multiplicity of muons, but rather their impact parameter. Pythia might be off with the b mass, with the B baryon branching ratios, with a number of things, but I doubt that they have B lifetimes one order of magnitude too small.

Essentially, the B cross section has been measured with care using secondary vertices, and once that is proven to be in good agreement with QCD, one can isolate the longer-lifetime component with ease. In the plot above (the first one), all the B’s have died out by the time the impact parameter reaches 0.5 cm. So, it is really not possible that what is seen is B or prompt QCD. If an explanation exists in terms of SM physics, that is some weird combination of factors involving punch-through and nuclear interactions. Pasha Murat, who commented above, studied the effect and he claims that the “ghost” muons are hadronic backgrounds in high-energy events. I think he is on the right track, but it remains unconvincing because the large majority of ghost events are not coming from very energetic events. I think he gets the closest to the heart of the matter when he says “when one is not using identification cuts, his” [or her, Pasha] “analysis sample is dominated by difficult to quantify background”.


65. CDF multi-muons, hmm « Charm &c. - November 4, 2008

[...] 4, 2008 So I’m way behind the bloggy curve on this one (e.g. here and here), but I thought I would at least read the paper before talking about it.  The CDF [...]

66. Gordon Stangler - November 4, 2008

This is some really interesting physics, part of me hopes it becomes more then the Higgs kerfluffle from yesteryear.

PS: I linked you in a post of mine, but I don’t know how to use trackback yet. I hope you don’t mind.

67. Steve D - November 4, 2008

I am a member of the general public and thus, this comment is massively off-topic, but I feel there is something worth saying. Both this fascinating blog entry and the following comments are a tribute to the robust health of this area of science. It breathes of the dedication, the intellectual rigor, and balanced conservatism of you all. …And something else too: It shows the humanity of a wonderful community of scientists who roundly deserve to be called ‘elite’. I shall wait in great anticipation of the final verdict on this anomaly.

68. dorigo - November 4, 2008

Hi Gordon,
it’s fine, never mind – I think trackbacks are automatic, but I do not care about those anyway. I get notified by wordpress bots when somebody links me, however.

Hi Steve,

thanks for visiting. No, it is not off-topic. Particle physics is a healthy scientific discipline, despite the cuts in funding experiments and projects. Yes, we are sceptics. A century of excitements and failures has taught us to be. Believe me, you are not alone in watching this and looking for the last word on this.


69. ¿Viola el Tevatrón la “otra” ley de Pauli? Los bosones se descubren en Europa, los fermiones en América « Francis (th)E mule Science’s News - November 5, 2008

[...] y por Daniel de Eureka quienes me han llevado con sus hábiles manos a Peter Woit, John Conway, Tommaso Dorigo, Luboš Motl, Carl Brannen, Matti Pitkanen, Adam Falkowski, Geoff Brumfiel, y a algunos otros. [...]

70. supermaz - November 5, 2008

I’m amazed

71. erhard seiler - November 5, 2008

read this!

72. Alejandro Rivero - November 7, 2008

(a remark about my #39 above: great part of the stability of B decays comes really from its CKM term; this is not seen explicitly in the plots)

73. Hello world! « How the World Works - November 10, 2008

[...] Here is more detail from one of the experimenters: CDF publishes multi-muons!!!! [...]

74. Like Stepping Into a Whole Different Intartube | Screaming Planet - November 10, 2008

[...] subjects to comment on something entirely bizarre. While browsing the web, I ran across this blog post. Reading the page, I started feeling a mounting sense of unease about the contents. Not about the [...]

75. An appetizer for the impatient lubologist « A Quantum Diaries Survivor - November 19, 2008

[...] explaining why Strassler’s estimate of the cross section of “ghost events” in the recent CDF publication is right, and I am [...]

76. Wouter Hulsbergen - November 19, 2008

Hi Tomasso,

I am trying to digest the paper for a discussion in our group in A’dam and I have two burning questions:
- How is the QCD contribution subtracted to obtain the ‘ghost’ distribution for muon impact parameters in figure 7 (the first figure above)? And for example for the D0 invariant mass in figure 4?
- To obtain a lifetime from the distributions in figure 26 (last pictures shown above), you’ll need a momentum measurement. How is the momentum of these candidates estimated? This is not described in the paper.

Thanks a lot,

77. Cullen T.M. McGough - November 20, 2008

Ok, sorry to interrupt the serious discussion, but I’m irritated.

I was reading Neal Stephenson’s new book and he mentions “quantum cross-talk” as a mechanism for the transfer of data between discrete cosmi in a polycosmic interpretation of the universe.

I happen to look up at a stupid poster of moon phases on the wall, and realize that if such a thing actually existed, higher density regions (like neutron stars) would have the greatest cross-talk. So I google “quantum cross talk” and get this blog.

Now. I only understand every 6th word you guys are babbling on about, but you seem to be talking about verified (sort of) tests that witness extra muons popping into this cosmos without source?

And, to make it worse, 80% of you are using avatar icons representing tiling problems, just like Stephenson’s obsessive polycosmos “Lineage” cult dudes.

Damn it, damn it.

Please try to avoid collapsing this cosmos into a singularity.

78. Cullen T.M. McGough - November 20, 2008

Oh, lookie there. The icons are auto-magic. How nice.

79. dorigo - November 20, 2008

Dear Wouter,

as far as your second question is concerned, I can answer it straight away: although not a rigorous procedure, the tail of the impact parameter distribution can be fit with f(d_0)=k \exp^{(-d_0/c \tau)}, extracting the particle’s c \tau with good precision, regardless of the particle’s momentum spectrum. That is because the impact parameter remains invariant for lorentz boosts: the larger the \beta \gamma, the longer the particle travels (by a distance L=\beta \gamma c \tau), and d scales accordingly.

As for your first question, I have an answer for you, but I prefer to check it with the author of the analysis, because there might be a subtlety and I do not want to mislead you, given that you will be making use of the information. I will get back to you shortly on that.


80. Elias Lopez - November 24, 2008

Hi Tommaso,

I have a question:
As far as I know, one of the motivations that led to the observation of this unexpectedly large sample of events with muons at CDF was the measurement of discrepant bb cross sections (I mean, discrepant with respect to the SM predictions).
In the paper by the CDF collaboration published in Phys. Rev. D 77, with reference 072004 (the one in that the “tight SVT cuts” are applied), I read that not only CDF reported a measurement of R2b (the ratio of the measured bb cross section to the exact NLO prediction) unexpectedly large (3.0+/-0.6), but also D0 (2.6+/-0.7).
As I understand (according to the paper just released by CDF), the origin of this value of R2b (at CDF) are the “ghost muons” that in a posterior analysis are cutted by the “tight SVT cuts”. And my question is: Does the fact that there has been another (independent, I supose) measurement of R2b at D0 consistent with the one obtained by CDF support the idea that the observed “ghost muon sample” is really new physics, and not a failure in the analysis?
Thank you very much,


81. dorigo - November 24, 2008

Hi Elias,

I think the D0 measurement is 2.3+-0.7, not 2.6.
In a sense, yes, it is an indication that D0, were to do the same analysis, would probably find some excess too. However, while CDF has measured the bb xs with both SVX and dimuons, D0 has done it only with dimuons. If D0 found a number close to NLO with secondary vertices, that alone would be some indication that they too have a unknown extra source of muons.

Whether that is new physics or some screwup in the simulation of energy loss and other effects in the material, is not granted though.


82. dorigo - November 24, 2008

… To clarify: if there is a bug in GEANT, it might affect both detectors equally. If Fermilab received a batch of iron which is iron-plated aluminum, both detectors have less material than they expect, and more muon fakes. There are dozens of ways a correlation may exist between the counting of muons in D0 and CDF… All quite improbable, but if compared to the new physics we are talking about… Well…


83. The whisper of the universe « The Gauge Connection - December 1, 2008

[...] for too long. Whoever is interested about the relevant discussions about I just point you to the Dorigo’s blog being him one of the authors of the CDF’s paper. This provoked a lot of rumors in the [...]

84. A chat with Arkani-Hamed at CERN « A Quantum Diaries Survivor - December 9, 2008

[...] This caused arguments -better call them exchanges- with Neal Weiner and with Nima Arkani-Hamed (see here for the original epistolary). Nima, in particular, had a remarkable incipit in his comment to my [...]

85. Yet another leptonic excess. (MiniBooNE) « High Energy PhDs - December 15, 2008

[...] us a speculative “multi-muon anomaly” at CDF (arXiv:0810.5357, see also Tommaso’s summary), the publication of the PAMELA cosmic-ray positron excess (arXiv:0810.4995, ), and related [...]

86. Shantanu - January 21, 2009

Coming back to the question whether neutrino mass is evidence for physics beyond standard model, please see the abstract of this lecture
series at MIT
by J. Conrad.

“Neutrinos vs. the Standard Model: Because Goliath Lost!”
Prof. Janet Conrad
Over years, physicists developed a “Standard Model” of particle physics which describes the data very well. It correctly predicted the results of nearly all particle physics experiments. Now we think the tiniest matter particle, the neutrino, shows a chink in the Standard model. This talk describes the discovery of neutrino mass and discusses the next steps in neutrino physics world-wide and at LNS.

dorigo - January 21, 2009

Hi Shantanu,

I know Janet well, and she is a sort of taliban of neutrinos ;-) Seriously, she would have been my first choice had one asked me to name somebody who thought that neutrino masses were evidence of BSM physics. But things are not as simple as she paints them. The SM is still there, and as I said somewhere in this blog already (here),

“The neutrino masses force an extension of the Standard Model more or less as revolutionary as a rearrangement of the furniture in the kids’ room forced by the arrival of a new baby.“


87. That crazy leptonic sector: multi-muon model-making « High Energy PhDs - February 16, 2009

[...] the best `armchair’ reading on the multi-muon anomaly is still Tommaso’s set of notes: part 0, part 1, part 2, part 3, part 4. An excellent theory-side discussion can be found at [...]

88. EnjoyMedia - March 17, 2009

Nice post.

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