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No discussions on CDF/PAMELA yet?

  1. Nov 1, 2008 #1
    I find the recent results from those experiments quite interesting and it is somewhat disturbing not to see any comments on them here at BTSM/PF... :bugeye: I am not expert, but would like to read well-informed summaries and discussions of the results. Of course, a careful reading of the papers and the relevant literature takes time.
  2. jcsd
  3. Nov 1, 2008 #2


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    In defense of our Beyond forum I should point out that I started a PAMELA thread about two months ago, on 3 September.

    And Cirelli himself came and posted on the thread. Our discussion went on for over a dozen posts.

    I proposed to Cirelli that if his Minimal SM extension explaining the PAMELA results should turn out to be confirmed, that he should name the Dark Matter particle after me, Marcus, and call it the marcon. :biggrin: For some reason he chose not to reply. Perhaps he is reluctant to consider that name out of personal modesty, because his own name is Marco.

    I will bump that September PAMELA thread in case there is interest in further discussion of whatever aspects.
    Last edited: Nov 1, 2008
  4. Nov 1, 2008 #3


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    As to the controversy around the CDF report, I was waiting for some collider-minded person to initiate a thread. Peter Woit found record that the CDF group was already having lengthy discussions back in June and July about whether they dare breathe a suggestion that they'd found a new particle. They finally decided not to voice that implication.

    So it's still pretty foggy. The hopeful story is that proton and antiproton collide creating a b+bbar pair (a bottom quark and its antiquark brother). Then each of these decays into a muon almost immediately, before it has a chance to travel even a millimeter. So the signature should look like two muons departing from somewhere inside the 3 centimeter pipe.
    But according to the hopeful story, it looks like one of the quarks might sometimes change into something else with a longer lifetime which is able to go thru the wall of the pipe before it decays into a muon. Because they have observed some thousand or so events where there is a pair of muons but one seems to originate outside the wall of the pipe, rather than inside as was expected.

    At present there is this hot discussion of whether the hopeful story is right (and there is some unkown intermediary particle longlived enough to go the extra centimeter or two before decaying) or whether there is some less interesting explanation.

    And one can say that most of what we are learning is about the psychological character of various people in the community. Who wants to show they are skeptical and conservative and who is willing to jump up with ideas. One is learning how wonderful Tommaso Dorigo and the Jester of Resonaances are as bloggers. Because they have really informative discussions of all this. But so far I don't feel that I am learning anything new about nature yet.

    Maybe someone else has some insight into the CDF business, and will comment.
    Last edited: Nov 2, 2008
  5. Nov 1, 2008 #4
    Several bloggers have already jumped on the topic.

    I read Peter Woit's entry first, but also Lubos and Tomasio Doragio have postings on the subject.

    I think Woit is mistaken in his analysis that the Nima/Weiner paper that predicted lepton jets with invariant mass of a few GeV (which is more or less exactly the signal that CDF sees). Woit says something about the model not being a SUSY model, but Lubos points out that the models only make sense in the context of SUSY. Basically, there are a bunch of light scalars floating around. Anytime one has light scalars, you need SUSY to explain why the scalars are light. (I'm just repeating Lubos' argument here, as I haven't read and understood the papers myself.) So if it is true that the model has light, fundamental scalars, then Lubos is right and the model needs SUSY.

    Of course, the reason that you haven't seen any threads on the subject is that most physicists (that I've talked to, at least) are pretty skeptical of the result. My boss was quick to point out that there have been exciting signals like a higgs at 160 GeV, from a tau excess last summer:


    So, mostly people are trying not to get their hopes too high, before someone comes along and explains the data in a more convincing, and less exciting way.

    As for PAMELA, it's more or less old news. Basically they see too many positrons a the end of their spectrum, but people are also skeptical of this result because it's hard to differentiate positrons and protons at these energies (both particles are effectively massless). Of course, the PAMELA people claim that this isn't a problem, but theorists are pretty jaded by 25 years of confirmations of the standard model.
  6. Nov 1, 2008 #5


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    Theres not much more to be said about anything yet. Nima/Wiener or others will need to make something more quantitative and make a more rigorous/encompassing and specific model that fits the data the best. Presumably that should be pretty straightforward (its not a particularly difficult or radically new outline relative to what people have studied before) but you never know, sometimes there are pitfalls in unexpected places in phenomenology.

    Meanwhile the CDF people should be busy checking and rechecking sources of error and alternative and more mundane hypothesis. Atm if I had to guess, i'd say the excess will go away, or be explained by something less exciting.

    The next step is for D0 to look at their data, as Tommaso indicates this is also challenging b/c of their particular setup, but will be done nonetheless. Etc etc etc, people are already hard at work on this and the wheels are now working, and i'd expect a flood of activity in the next few days/weeks/months on the subject.
  7. Nov 2, 2008 #6
    Here's a prediction:

    Look for a flood of papers from China about collider signals :)
  8. Nov 2, 2008 #7
    Dear BenTheMan,

    yes, the light scalars need SUSY. That's why Nima and Neal came to the idea to add supersymmetry to a previous model. But this only explains why their search was not a coincidence but a rather systematic piece of work.

    Another question is what signals they predict for the colliders. Even if you swallowed a non-supersymmetric model with light scalar masses, you couldn't predict any lepton jets. The lepton jets arise as a prediction that depends on other features of supersymmetry such as the existence of the lightest supersymmetric particle (LSP) and especially the LSP among the particles of the minimal supersymmetric standard model (MSSM).

    It's the MSSM LSP that helps to create the lepton jets etc. One could perhaps replace the SUSY model with a model that has something instead of the MSSM LSP but such a model would probably be fine-tuned at way too many levels. It's not just about the light scalars. One would have to adjust many more properties of the new particles to make it look like SUSY. To summarize, the non-supersymmetric models generically predict that there should be no lepton jets.

    So if this explanation of the PAMELA, CDF dimuon, and other observations were right (which is a huge "if"), it would be an extremely strong circumstantial evidence for SUSY and, in fact, also other typically stringy signatures such as the existence of a hidden gauge theory sector and a quiver structure of matter fields. It would be just a small simplification to say that it would be an experimental proof of string theory. Still, it would be just a beginning in finding out the right compactification that actually gives these signatures in detail.

    Best wishes
  9. Nov 2, 2008 #8
    Hi Lubos---

    This is why I thought that Peter Woit's statement sounded bogus.

    Well, this is too strong a statement, in my humble opinion. Getting weak scale SUSY and another gauge group are both good things for string theory---it has been my experience that these are pretty generic predictions for almost all classes of string vacua, and it may actually make stringy model building easier. Proof of the Neal-Nima model (or even experimental support) will probably garner these two guys a Nobel prize, but Green, Schwartz and Witten will be watching the ceremony on TV.
  10. Nov 2, 2008 #9
    Dear Ben,

    well, Nobel prizes have sociological rules, but from the viewpoint of science, a particular SUSY model - and so far, we are not talking about an explicitly defined model with details - is just a tiny technicality relatively to the whole framework of SUSY, and I am certain that Nima (and probably Neal, whom I don't know well) would agree that in this case, they were just people playing on the shoulders of giants. You know, the purpose of physics research is not to get Nobel prizes.

    Nobel prizes is how the laymen may measure the importance of things but it's not how physics professionals do it. I tend to agree that the down-to-Earth discoveries would win the first prize(s). Green, Schwarz, Witten would surely be happily watching on TV and Nima would surely give a talk containing some memes written in these paragraphs of mine.

    You know, if this model is correct, the LHC is very likely going to see the superpartners, inducing a lot of other opportunities for your favorite Nobel prizes and moving the mankind's knowledge much closer to the universal picture of string theory. If some dirty phenomenological model of SUSY hidden sector is correct, be sure that it is not the last word of physics.

    Please learn how to spell the name of John Schwarz.

    Best wishes
  11. Nov 2, 2008 #10

    Perhaps it was not clear that I was exaggerating. Either way, the point that I was trying to make is that superpartners and another gauge group are great evidence for string theory, though not proof in the canonical sense. I could equally well imagine poorly motivated, finely tuned models that gave me the same signature.

    Apologies of course :)
  12. Nov 2, 2008 #11
    Thank you for your responses.

    Back in 2000/2001 I was investigating (w/ some collaborators) self-interacting DM scenarios. Based on this paper:


    and this one (unavailable online):


    as well as others indicated in the references (see attachment in poster pdf format), we had some preliminary results, which nevertheless were never published. I never got back to this, but now I would be interested to know from a particle physicist whether the limits we have reached at (from a completely different route and under different assumptions) are reasonably interesting in the present context. This is just curiosity; I do not intend nor have the energy to get back to that work. Nor am I updated on the current constraints from self-interacting DM, so perhaps our results could have already been ruled out by now, I can't tell. I'd be glad to receive some input from someone updated on this, you may send me an email christinedantas<at>yahoo.com if that is the case.

    I admit to be skeptic but interested to see what will result from the various upcoming analyses on CDF and Pamela, specially the former.


    Attached Files:

  13. Nov 2, 2008 #12


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    Christine, a curious detail. We learned today from Tommaso
    that 33 percent of the CDF people refused to sign the article.

    Since the article was worded so non-committally that there seemed to be no chance of embarrassment whatever happened, why would they not choose to share the glory in the unlikely case that the tentative results prove significant? A third of the insiders seem more doubtful of their own result than even the most skeptical outsider.
    Last edited: Nov 2, 2008
  14. Nov 3, 2008 #13

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    This whole thread amuses me. There was a post in HENPP on the CDF result before the complaint here that nobody was talking about it, and the curious detail you "learned today" was posted there on Halloween.

    You guys have to get out more! :wink:

    You may not get a CDF member to explain why they didn't sign the paper. If their reason, whatever it is, involves as-yet unpublished data, they may not want to say anything.
  15. Nov 3, 2008 #14
    Probably the reason has something to do with the picture I posted above :)
  16. Nov 3, 2008 #15


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  17. Nov 3, 2008 #16


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    Phenomenological interpretation of the multi-muon events reported by the CDF collaboration
    P. Giromini, F. Happacher, M. J. Kim, M. Kruse, K. Pitts, F. Ptohos, S. Torre
    6 pages, 9 figures. Submitted to Phys. Rev. D. Rapid Communication
    (Submitted on 31 Oct 2008)

    "We present a phenomenological conjecture of new physics that is suggested by the topology and kinematic properties of the multi-muon events recently reported by the CDF collaboration. We show that the salient features of the data can be accounted for by postulating the pair production of three new states h1, h2, and h3 with masses in the range of 15, 7.3 and 3.6 GeV/c^2, respectively. The heavier states cascade-decay into the lighter ones, whereas the lightest state decays into a tau pair with a lifetime of the order of 20 ps."

    Woit comments:
    "...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..."

    See also Dorigo:
    Last edited: Nov 3, 2008
  18. Nov 3, 2008 #17
    So we have an obvious way to double-check the CDF results-- see whether D0 sees the same effect. But is there any other experiment current or planned which can confirm or dispute the PAMELA data?
  19. Nov 4, 2008 #18
    We should distinguish between phenomenological and theoretical explanations in that the former are ad hoc and thus incomplete whereas the only idea we know of that naturally explains these results - if they are the real deal - on the foundational level is supersymmetry.
  20. Nov 4, 2008 #19


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    The activity on Hep-Ph and Hep-th in the last two days reminds me of the craze after Howard Georgi's Unparticle paper. Or how, best to write a paper that will guarentee citations in 4 days with nothing but an overdose of caffeine. Of course, you are encouraged to forget the papers in question after properly citing, tyvm!
  21. Nov 4, 2008 #20
    The over-under on the first un-particle explanation of the CDF data is two weeks.

    I'm putting my money on the under.
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