The Circus Begins

Friday’s arXiv posting of the paper by CDF about the multi-muon anomaly they are seeing has already generated three different conjectural explanations of what physics might be responsible for this. Undoubtedly many, many more are on the way.

  • Some members of the CDF collaboration have posted a paper entitled Phenomenological interpretation of the multi-muon events reported by the CDF collaboration. This explains the large numbers of muons with a rather baroque mechanism, conjecturing the production of a 300 GeV heavy particle decaying through a chain of 3 lighter particles, the last of which is supposed to be the long-lived (20 picosecond) one. This interpretation was part of the original draft PRL from last June/July. The CDF collaboration as a whole seems to have decided not to support the draft PRL and this interpretation, instead releasing just a PRD paper that describes the anomaly without trying to interpret its significance. It also seems that only two-thirds of the collaboration put their names on the PRD paper, and the interpretation paper was put out just by a small group. The whole story is somewhat reminiscent of the “Superjet” affair (see Tommaso Dorigo’s multi-part discussion here), which also involved a PRD publication about an anomaly signed by the collaboration, and an interpretation (in terms of squarks) signed by a much smaller group led by Paolo Giromini.
  • An hour or so after the Giromini et. al. paper came in on Friday, a group of string theorists had posted the 40-page Towards Realistic String Vacua on hep-th claiming to explain the CDF results with a class of string vacua:

    We also describe model-independent physical implications of this scenario. These include the masses of anomalous and non-anomalous U(1)’s and the generic existence of a new hyperweak force under which leptons and/or quarks could be charged. We propose that such a gauge boson could be responsible for the ghost muon anomaly recently found at the Tevatron’s CDF detector.

    If the Giromini et. al. explanation invoking 4 new particles is baroque, it’s hard to know what the right word is for the far more complicated constructions that are described in this paper.

  • There’s a new version this evening of the 3-week old Arkani-Hamed/Weiner LHC Signals for a SuperUnified Theory of Dark Matter, in which they claim to have a new signature for supersymmetry, with a large fraction of all SUSY events looking exactly like what CDF described. Oddly enough, the changes to the paper don’t include a mention of the CDF result. This paper also invokes a rather baroque mechanism, involving both the supersymmetric extension of the standard model and a whole new complicated dark sector.
  • This last paper is also supposed to explain the PAMELA data, and papers with other explanations of this are starting to flood hep-ph.

    So far, all the explanations of the anomaly seen by CDF look suspiciously complicated, which may be one reason that many members of CDF are so skeptical about the whole thing that they were unwilling to sign on to the PRD submission. But I’m sure that many more proposals for how to explain the anomaly are being drafted at this very moment, and maybe one of them will be more convincing.

    Update: Over at Tommaso Dorigo’s blog there’s a short posting about Giromini et. al., and an exchange with Nima Arkani-Hamed, who claims to have had no inside knowledge of the CDF “lepton jets” when he wrote his paper with Weiner predicting them. He also explains how the exact mechanism discussed in that paper is unlikely to explain the CDF result since their observed rate is too high for this.

    Update: New Scientist has the story, emphasizing the possible relation to the work of Arkani-Hamed and Weiner:

    So what could it be? As it happens, Weiner and Nima Arkani-Hamed of the Institute for Advanced Study in Princeton, New Jersey, and colleagues have developed a theory of dark matter – the enigmatic stuff thought to make up a large proportion of the universe – to explain recent observations of radiation and anti-particles from the Milky Way.

    Their model posits dark matter particles that interact among themselves by exchanging “force-carrying” particles with a mass of about 1 gigaelectronvolts.
    The CDF muons appear to have come from the decay of a particle with a mass of about 1 GeV. So could they be a signature of dark matter? “We are trying to figure that out,” says Weiner. “But I would be excited by the CDF data regardless.”

    CDF spokesperson Jacobo Konigsberg is quoted as saying:

    we haven’t ruled out a mundane explanation for this, and I want to make that very clear

    Update: Then there’s Slashdot, where the hypothetical CDF particle is advertised as accounting for the Arkani-Hamed et. al. theory of dark matter.

    Update: Another story, at Physics World, which has more from various people at CDF. Again, that Arkani-Hamed/Weiner “predicted a CDF–like signal”, although the problem with the rate being too low is mentioned.

    Also Nature, where one learns:

    Theorists are already coming up with ideas about what might be producing the excess muons. One possibility is that they stem from the decay of a heavier, yet-to-be-discovered particle — perhaps related to dark matter, an unseen material that is believed to make up some 85% of matter in the Universe.

    Another idea from string theory evokes seven-dimensional ‘branes’ — theoretical surfaces that are inhabited by exotic particles manifested as strings. These higher-dimensional branes might be home to force-carrying particles that interact weakly with our three-dimensional world and create a faint, but traceable, signal in the data.

    But Adam Falkowski, a theorist at CERN, Europe’s particle accelerator laboratory near Geneva, Switzerland, says that the explanations need some work, and cautions against attempting to force the data to fit into particular theories.

    Update: More press stories here and here.

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    24 Responses to The Circus Begins

    1. onymous says:

      A 300 GeV particle with a 100 nb cross section. That’s… special.

      (They don’t need the 300 GeV particle; they need the 15 GeV particle, but with enough of a boost to have collimated decay products. Hence the ad hoc 300 GeV Higgs to fit the curves.)

    2. Coin says:

      So far, all the explanations of the anomaly seen by CDF look suspiciously complicated, which may be one reason that many members of CDF are so skeptical about the whole thing that they were unwilling to sign on to the PRD submission

      Hm, maybe I don’t understand what you’re suggesting here… is it normal for experimental particle physicists to doubt experimental results to the point of not participating in their publication, just because they can’t find a clean theoretical mechanism from which those results came?

    3. Roger says:

      Its very unusual for a collaboration member to remove his/her name from a paper though it does happen from time to time.

      However, I have never heard of a third of a collaboration removing their names. This is very worrying.

    4. Peter Woit says:


      If your experiment is seeing something confusing and completely different than what known theory predicts, the chances are quite high that the problem is with your experiment, and every experimentalist is well aware of this. On the other hand, if the 20ps state CDF is seeing evidence for had the right properties to be the SM or MSSM Higgs, I’d bet absolutely everyone in CDF would have signed on, the paper would be a PRL making a discovery claim, and CDF leaders would be ordering their outfits for a trip to Stockholm.

    5. James says:

      There’s a quote I’ve heard attributed to Einstein that goes roughly like “A theory is something believed by nobody except its creator, and an experiment is something believed by everybody except the experimenter.”

    6. Shantanu says:

      Peter or anyone else, does anyone know what this model predicts for
      proton decay? This might be a good way to test the consistency of these

    7. Peter Woit says:


      Which model? I don’t think any of the models discussed here is the sort of thing that would make a testable prediction about proton decay.

    8. Sumar Ongi says:

      My personal hunch —as if it mattered— is that this whole thing will fizzle out. This is not a criticism of CDF and of the theoreticians working on this issue (quite the opposite, I see their work with respect and even admiration). It’s just how physics works: 99% blind alleys, 1% breakthroughs.

      Now, a 300 GeV Higgs boson? I would love so much to see that!!!

    9. Pingback: News from the CDF and PAMELA experiments « Theorema Egregium

    10. dragon says:

      “Then there’s Slashdot, where the hypothetical CDF particle is advertised as accounting for the Arkani-Hamed et. al. theory of dark matter.”

      Taken literally, this statement means that the CDF observations explain the existence of certain papers, rather than the other way around. One suspects a typo at first, but in view of what has been going on over at Dr Dorigo’s blog, perhaps this is the right ordering after all…….

    11. Lol dragon… I decided I will not investigate the matter further. We have heard from the theoreticians, we know the story, the documents are out there for anybody to make their own mind. And regardless of opinions, publications remain.

      My own opinion is however the following:
      1) the CDF signal is not NP
      2) the NAH et al. papers discuss an interesting signature, which however does not describe reality
      3) we are still in the dark and we will stay there for a while
      4) I am going to collect 1000$ soon. How soon ? Depends when the LHC will deliver 10/fb of data.


    12. Arnaud says:


      I’m not a professional physicist so pardon my naivete: How can anybody have a theoretical explanation for what appears to be a quite unexpected experimental result, less than a week after its publication? I’m sure HEP is full of very bright people, nevertheless this looks a bit rushed to me, and suspiciously like a race to publish.

      Personally, my only way of understanding this would be if either the news have been in the pipeline beforehand, or it was in fact expected. The blog hasn’t mentioned either fact, I think?

      Physicists like to mock the media and their rush to the “story” over scientific content, but from the outside this particular event looks like this story of pots, kettles and blackness… Or am I wrong?

    13. Peter Woit says:


      There’s plenty ot mock about the media’s coverage of science, but my own point of view is that in recent years the blame for problems with media coverage of some parts of physics lies with physicists themselves rather than journalists.

      This experimental result was not expected at all by theorists. It is not known how widespread knowledge of the CDF result was before it was released last Thursday evening. Back in July, people at CDF were already worried that the news had leaked out (how do I know this? because by mistake the documents of their internal deliberations were freely available on-line and indexed by Google.)

      One of the papers mentioned above appeared within a day of the Thursday evening news. My own view is that the paper in question uses a typical string theory set-up that is capable of explaining anything. String theorists are hard-working and industrious, it’s perfectly plausible that within 24 hours they could have drafted the section of the paper needed to “explain” the CDF result within the context of the string theory models they are working with. In the same 24 hours they undoubtedly could have come up with explanations of all sorts of different unexpected experimental results.

      This all shows what is likely to happen if and when unexpected preliminary result come out of the LHC. String theory/supersymmetry explanations of the results will come fast and furious, no matter what they are.

    14. Peter Woit says:

      In case the above is unclear, I’m referrring to the second paper mentioned in the posting. The first is from within CDF, the authors have had many months to work on their analysis. The last one is a paper written before the results were announced, there is extensive discussion about it over at Tommaso Dorigo’s blog.

    15. Chris W. says:

      This all shows what is likely to happen if and when unexpected preliminary result come out of the LHC. String theory/supersymmetry explanations of the results will come fast and furious, no matter what they are.

      It will be a painfully protracted process of coming to see not ST/SUSY’s inability to explain these results, but its inconclusive and ultimately sterile fecundity* in explaining them, along with a million other results we don’t happen to see, for reasons that will receive their own convoluted explanations (if anybody cares).

      [* or to use Kant’s phrase, “accursed fertility“]

    16. Pingback: ¿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

    17. Arnaud says:

      Thanks Peter & Chris. I am not participating constructively to the discussion here, but instead I have another question, sorry again.

      You seem to imply that String theory is an elastic concept which can
      be made to fit any new fact and sort of retroactively claim that some form of it predicted the result, right? I’m kind of an educated layman on this (I’m only an actual rocket scientist), but I read Lee Smolin’s book, so I guess I’m convinced by your argument now 🙂

      My question is slightly different here: People like you and Lee seem to argue that over the last 20 or 30 years, not much has happened in theoretical particle physics, due in part to the lack of experiments (like the LHC) probing deeper into the high-energy spectrum. This seems to leave plenty of time to researchers to analyse current gaps in detail and hone their predictive models or new theories.

      When I match that to some papers and presentations I’ve seen where different explanations are proposed depending on different expected values or results of proposed experiments (such as the mass of the hypothetical Higgs Boson), It leads me to imagine that there are a bunch of -to caricature- “if-then-else” set of explanations and theories ready to be put out as soon as new results come in. Does that make sense, and would you say it’s in any way correct, or is the picture not quite like that?

      This was how I though one could explain fast turnover of papers, although you’re clear in your response it doesn’t apply here because the results are quite unexpected. I guess this is what makes fundamental physics interesting!

      PS, I read Tomaso’s futher post and loooong dialogue and comments on this. I can’t claim to have an informed opinion, but it leaves me a sad impression that the discussion is as much about physics as it is about ego and politics.
      I recognise though, it takes a strong dose of wisdom and character to stand up for scientific integrity in this world of inflated career expectations, performance-related-pay and short-term contracts. I guess they don’t teach those in physics courses… (This comment could be made for a lot of disciplines, naturally).

    18. Thomas D says:

      It is actually very disappointing that experimentalists would effectively refuse to publish a 10 sigma deviation, even after all imaginable systematics and loopholes are investigated, just because it is difficult to find a theory (within conventional frameworks) to account for it. But I don’t know the exact reason why the whole collaboration would not sign up to the long Phys Rev paper.

      The quote about ‘theory is believed by no-one beyond its creator’ is not at all true nowadays. On the contrary, HEP experimentalists are very reliant on theorists to tell them what types of signals are ‘likely’ to emerge (meaning, likely given some popular model or theory). That means that if none of the popular theories are right, the experimental search will not be well set up to investigate what there actually is.

      There are a few groups trying to put together a ‘model-independent’ search for new physics at LHC, which is a good insurance policy against all the theorists being wrong, but maybe not enough attention is being paid to this.

      Any reporting that tries to link the muons to recent dark matter models is pretty much malpractice. Arkani-Hamed has written:
      “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! (…)”

      I am not sure what Peter is blaming physicists for in media coverage. Is he saying the Quevedo group is too hardworking? I have to say also, they are relatively lucky, since contrary to what he is insinuating not all string models have these leptonic or ‘hyperweak’ U(1)’s readily available… and not all string theorists happen to have a 40-page paper ready to publish at the same time as experimentalists announce something.

      Perhaps someone could take the elementary step of asking someone in that collaboration whether or not their models can always explain every possible signal, rather than taking this as a basic assumption.

      And it’s by no means certain that this model *can* explain the multi-muons, rather than just containing ingredients which could go some way towards it. On p. 30 they say:
      “Notice that this proposal to explain the CDF data can be considered independently of string theory. While we have assumed U to be a gauge boson motivated by the D3-D7 brane models considered in this paper, the same basic phenomenological approach could apply for any bulk state with very weak couplings to quarks and no kinematically accessible 2-body decays. (…)
      It remains to be seen if with these numbers it is possible to obtain the proper U lifetime. The above is clearly a phenomenological scenario and not yet a full model. More detailed model-building is necessary for a full analysis of the merits and further phenomenological and cosmological implications of the approach outlined.”

      So again, what is Peter’s problem with this?

    19. Peter Woit says:

      Thomas D,

      CDF is not refusing to publish anything, they have submitted a paper to PRD. Some of the collaboration aren’t signing on to the publication for various reasons. For an experimentalist to be skeptical about a very weird signal, thinking it is likely to be a flaw in the analysis, so not ready for publication, isn’t exactly unusual or surprising.

      I don’t think I’m the only one who finds laughable the spectacle of a group of string theorists putting out a paper in less than 24 hours “explaining” a very weird and unexpected signal using a very complicated “string vacuum”.

    20. Peter Woit says:


      Thanks, fixed.

    21. If the Giromini et. al. explanation invoking 4 new particles is baroque, it’s hard to know what the right word is for the far more complicated constructions that are described in this paper.

      I know that this was ironic, but the word for the step up from ordinary baroque is churrigueresque — ‘frantically baroque’, as it has sometimes been called. I bring it up just because it’s sometimes a very good word to have on hand.

    22. Peter Woit says:

      Thanks Brandon, I’m always glad to learn a new word.

    23. Pingback: symmetry breaking » Blog Archive » CDF’s ghosts: The next step and speculation

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