Still Waiting for Supersymmetry

The headline story at the APS Physics site is Still Waiting for Supersymmetry, by Sven Heinemeyer, which reports on a PRL article from CMS reporting no evidence for supersymmetry.

According to Heinemeyer:

It’s important to realize that CMS’s results do not exclude supersymmetric theories. Rather, they only conclusively say one of two things. One possibility is that the CMSSM (the specialized version of the MSSM) is realized in nature, but the supersymmetric partner particles, the gluinos and squarks, are relatively heavy—too heavy to be produced in large numbers at the LHC so far…

The other interpretation is even simpler: while supersymmetry is realized in nature, it might not take the form described by the CMSSM, but possibly that of any one of the many (GUT scale) models. Different versions of supersymmetry make different predictions for the outcomes of high-energy proton-proton collisions. Many of these outcomes are more complicated than what is shown in Fig. 1, and to see them would require experiments to investigate many more collisions (and to study them for a longer time). Consequently, in these other models, it will only be possible to place much weaker bounds on the new particle masses (so far, however, no such dedicated analysis has been performed).

I would have thought that there’s an even simpler third alternative: no supersymmetry in nature at all, but I’m not a SUSY phenomenologist…

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41 Responses to Still Waiting for Supersymmetry

  1. neo says:

    Einstein was once asked what he would conclude had the evidence of the deflection of light by the sun not supported the theory of genral relativity. He answered something along the lines of “that would be too bad for the evidence, because general relativity theory is too beautiful not to be true.” Is SUSY too beautiful not to be true?

  2. M. Wang says:

    “It is difficult to get a man to understand something, when his salary depends upon his not understanding it!” — Upton Sinclair

  3. N. Nakanishi says:

    Neo

    General relativity was quantitatively confirmed by the perihekion shift of Mercury before the observation of the deflection of light. On the other hand, SUSY has absolutely no experimental support.

  4. Henry Bolden says:

    The supersymmetry debacle was predicted by the The Everly Brothers:

    Wake up, little SUSY, wake up
    Wake up, little SUSY, wake up
    We’ve both been sound asleep, wake up, little SUSY, and weep
    The movie’s over, it’s four o’clock, and we’re in trouble deep
    Wake up little SUSY
    Wake up little SUSY, well

  5. Bernhard says:

    That Sven wants to give SUSY the benefit of doubt is fine of course. Technically speaking he is correct (SUSY is indeed not excluded). But he is being deliberately misleading in not talking about the third possibility that SUSY might simply not be realized in nature and to say this out loud. All in all I think it is not nice APS asks a SUSY fanatic to talk about an article that is clearly not good for the SUSY idea without asking also an anti-SUSY person to make a counter comment in the name of keeping the discussion two-sided. This is not healthy.

  6. Cesar Laia says:

    Comments here are too harsh, I think. I am a layman, but I clearly see “…suggests that if the theory is correct, it may be more complicated to discover these particles than previously thought.”

    So, he states “if the theory is correct” and then goes on. I don’t see the problem with this.

  7. Bernhard says:

    Cesar Laia,

    Of course Sven did not forget the usual caveats, but this is in my opinion not putting all possibilities with the same weight. If we add the fact that the particular article he is talking about should lean to the possibility he does not explicitly discuss this is even worse.

  8. William Tell says:

    Time will tell and put everybody in place.

  9. Peter Woit says:

    Cesar Laia,

    What you’re quoting is from the headline summary of the article, something which is normally not written by the author, but by an editor. The normal complaint is that physicists write something accurate, and the editor then hypes the story in the headline. Here, the physicist is writing inaccurate hype, and the editor is correcting the story in the headline.

    To be clear, I don’t think Heinemeyer is unaware of the logical possibility of no SUSY, but it’s psychologically interesting that he can’t bring himself to mention this in print.

  10. CIP says:

    Or perhaps the squark, like the snark*, is a boojum.

    *with apologies to Lewis Carroll

  11. Philip Gibbs says:

    Peter, he is not giving a list of all the logical possibilities. He is giving a list of the possible things that can be said “conclusively” from the CMS results. In the first sentence he makes this clear and he says explicitly that excluding supersymmetry is not on that list.

  12. Peter Woit says:

    Philip,

    I’m sure one can come up with a strained reading of the text involving unmentioned other “inconclusive” possibilities, and, again, of course Heinemeyer is aware of the non-SUSY case and would not deny it is possible.

    Still, I think a straight-forward reading of the text as written is that there are only two interpretations of the data he is willing to refer to explicitly and discuss: one is that SUSY partners are too heavy to see, the other is that they are hiding.

  13. Cesar Laia says:

    I made the remark because that headline looked to me as an abstract written by the author, not a feature added by the editor. And to me it is an useful statement about the point of view discussed further in the article. It looks like a good paper, anyway, although I am not a physicist so I miss details. The editors of that journal should consider to give an opportunity for other to express non-SUSY alternatives, no doubt. But that is not the problem of the author, I think, he expresses only is point of view.

  14. Philip Gibbs says:

    Peter, I am just reading it as it is written. It is your reading that is the strained one because you are always looking for your particular angle which is that the theorists are not willing to accept that supersymmetry has failed (which it has not yet).

    That angle is not there in this story. Nowhere does it imply that supersymmetry must be found. The bold line below the heading uses the phrase “if the theory is correct” . I can see nothing unbalanced there at all.

  15. Peter Woit says:

    Philip,

    People can read the thing and make up their own minds whose reading is strained. The only place you or anyone else has pointed to in the article that mentions the possibility that SUSY may not be realized in nature is the headline, which usually is written not by the author, but by an editor.

  16. SpearMarktheSecond says:

    Someone used to say… SUSY has no experimental support, but it has withstood the test of time.

    There are lots of contrived aspects of the current SUSY models… not one of them is as beautiful as General Relativity. But the non-GR part of the Standard Model is pretty darned ugly too… where does the ratio of the mass of the top quark to the mass of the up quark come from?

    The excitement of the LHC is like what Columbus and his crew must have felt when they sailed westward. And that is sufficient!

    What is distressing about the hype is that it has setup a sense of disappointment if SUSY is not there. I don’t care, the great value is in *knowing*, even if that is knowing that SUSY is absent at LHC mass scales.

  17. emile says:

    “It’s important to realize that CMS’s results do not exclude supersymmetric theories.”
    What if he had said: “I think it is important to realize that SUSY theories cannot be excluded.” I think that would have been more helpful to the reader…

  18. flog says:

    Flogging a dead horse? SUSY will never be disproved. Epicycles were never explicitly disproved. The luminiferous ether was never explicitly disproved. In both cases they just kept getting more and more contrived as new data came in. Also in both cases, an alternative theory came along which could do a better job of explaining the facts, and which did not require fine-tuning every time more data was found. People just lost interest in the outmoded clumsy way of doing things. SUSY will only go away when a new theory comes along that can explain things better. But there is no compelling alternative which does a better job.

  19. srp says:

    Do ellipses have fewer free parameters than epicycles (and equants and eccentrics?) That sort of inductivist criterion, while fine for assessing rival models within known-to-be-stationary, common data generation processes (such as pattern-recognizing neural nets), flops for comparing theories with non-stationary or overlapping but distinct predictive domains. The theory that the farmer loves the chicken and that his morning visits are for feeding purposes parsimoniously explains the data right up until the chicken is fat enough and gets slaughtered. Then the more complex theory that the farmer has extrinsic reasons for feeding the chicken looks a lot better, even though it has a lot of free parameters about how fat the chicken should be depending on prices for feed and for chicken parts.

    I’m sympathetic with our host, but a lot of non-systematizable judgment is needed in order to decide when more theoretical complexity is called for.

  20. N. Nakanishi says:

    Certainly, SUSY may be beautiful mathematically, but as a physics, it is evidently violated very badly. There is no Nambu-Goldstone fermion. If one wishes to use the super-Higgs mechanism, one has to introduce supergravity. However, quantum supergravity is a very ugly theory! There is no SUSY-invariant gauge fixing. The SUSY anticommutation relation for global super-charges no longer holds because of index mismatch (Note that gamma matrix is a local quantity; there is no global quantity having the same set of indices as gamma matrix in the framework of supergravity).

  21. Shantanu says:

    Peter, is there a similar sentiment on extra-dimension models or people have resigned
    to the fact these are all ruled out.
    (I asked this question to Lisa Randall when she did a guest post on cosmicvariance, but didn’t receive any response),

  22. Sven says:

    Hi,
    I feel I should also say a few words here… ;-)

    The journal asked me to write a layman explanation of the CMS paper, which deals
    with the search for SUSY. They did not see any excess and set limits. The real question is how these limits are to be interpreted. Interestingly, many people draw wrong conclusions from this kind of limits. I tried to convey what these limits really mean. Nothing more, nothing less.

    Any negative search that sets a limit can of course be interpreted as an indication that the ‘object’ searched for does not exist. However, this was not the question here.
    On top of that, the consequence would be to consider that nothing beyond what
    we know for sure so far exists: no Higgs, no SUSY, no extra dimensions, … because the LHC did not see anything new so far. Not a very helpful approach in my opinion.

    On the other hand, I would be interested whether I succeeded to explain the consequences of the SUSY searches published by CMS in a comprehensible way.

  23. Peter Woit says:

    Thanks Sven,

    It seemed to me your article avoids mentioning the elephant in the room: not finding SUSY evidence of the sort many people were expecting does throw more doubt on the whole idea of TeV-scale SUSY. There really are three possibilities here worth mentioning, not just two…

  24. Pingback: Uncommon Descent | Supersymmetry: In the face of lack of evidence, the unthinkable third alternative is …

  25. Anon says:

    From logic there can be only two definitive resolutions on supersymmetry: 1) it exists (direct or indirect observation of behavior predicted by or indicative of it) or 2) it does not (every single variant and flavour of it has been disproven experimantally. Which would be an immensly daring task indeed). Everything in between would be little more than ideology exchanges between theorists’ camps (at least for a long long time before not yet disproven parameter space of supersymmetry would start drying up).
    Want something more productive? Sure, just come up with an alternative theory that would achieve at least the same results as SUSY with superior observability and testability in experiment!

  26. Peter Woit says:

    Shantanu,

    In the extra dimensions case I think very few people ever seriously thought these would be seen at the LHC. So the LHC results just move the bounds up, and in a few years when the LHC runs at full energy, there will be another jump in the bounds. This is all just what was expected, so no one is talking about it. One can of course keep going working on such ideas, saying the scale is just higher up, but there’s likely to be less interest in this.

  27. helvio says:

    Gauge coupling unification, which can be extrapolated from current data to be an exact match at some very high energy (unlike the prediction from the Standard Model as it stands), is experimental evidence albeit indirect. Explain that without SUSY, in a simpler way.

  28. archytas says:

    Here is something that might amuse you all.

    I was re-watching the Elegant Universe the other day, and I noticed that Brian Green explicitly states that supersymmetry is a “central prediction of string theory.”

    If you want to find the quote, it is in the latter part of the program when they talk CERN.

  29. Eric says:

    Supersymmetry is a prediction of string theory since it is inconsistent without it. However, this does not necessarily mean low-energy supersymmetry which is observable at the LHC or other colliders. As far as string theory is concerned, supersymmetry can be broken at any scale below the string scale. So, if SUSY is not observed for LHC, this has absolutely no implications regarding whether or not string theory is correct.

    The reason for believing in low-scale supersymmetry is that it may allow several phenomenological issues relevant to the Standard Model to be elegantly resolved. These issues are the stability of the Higgs mass against quantum corrections, the apparent unification of the gauge couplings, and a natural dark matter candidate. The existence of a light Higgs boson which is an elementary scalar and low-energy supersymmetry are really tied together.

  30. Beelzebud says:

    It just strikes me as rather convenient that people declare SUSY as a central prediction of string theory, and then also say that if SUSY isn’t found that is has absolutely no implications for string theory.

    I don’t have to be a genius to see the problems with this. After awhile it just looks like a classic case of moving the goal posts around, every time you don’t get the results you hoped for.

  31. Eric says:

    Beelzebud,

    You seem to be missing the fact that, although supersymmetry is a necessary component of string theory, the scale at which it is broken is not fixed. Supersymmetry may only be observed at the LHC if it is broken at a relatively low scale. If it broken at higher scales, it will not be seen. As I stated, there are phenomenological reasons for believing in low-scale SUSY which have nothing to do with string theory. If SUSY is observed at the LHC, then this will provide support for string theory, but does not prove that it is correct. One can have supersymmetric point particle theories without any connections to strings. Conversely, the non-observation of supersymmetry at the LHC would only show that SUSY is broken at a higher mass scale, if it exists.

  32. Peter Woit says:

    Eric,

    The problem is that, in places like Brian’s NOVA series, the public was told something like “string theory does make predictions: it predicts supersymmetry, and this will be tested at the LHC”. One can be sure that if SUSY had (or does…) show up at the LHC, string theory enthusiasts would be vigorously claiming it as a confirmation of a string theory prediction. Not telling the public that no SUSY at the LHC was fine for string theory, since string theory really makes no predictions of the usual sort, was kind of misleading. I think the people doing it did believe that SUSY was likely to show up at the LHC and they would be vindicated. Now they’re trying to get away with claiming it wasn’t a real prediction. There’s an obvious attempt here to have it both ways…

  33. Eric says:

    Peter,

    The statement, “string theory does make predictions: it predicts supersymmetry, and this will be tested at the LHC” is technically correct. It does predict supersymmetry and this can be tested at the LHC, so I really don’t see your problem. You seem to be incorrectly interpreting this statement as saying that string theory predicts that supersymmetry should be observed at the LHC. If string theory is correct, then supersymmetry might be observed at the LHC, which is much different than saying that it predicts that it should be seen.

    If supersymmetry is found at the LHC, then this would indeed constitute evidence in favor of string theory, although it does not prove it is correct. However, you cannot claim that the a non-observation of supersymmetry disproves string theory since string theory minimally only requires unbroken supersymmetry at the string scale.

  34. Eric says:

    Also, it should really be pointed out that the expectation of seeing supersymmetry at the LHC comes from particle phenomenology rather than string theory. I do think that you have a tendency to give people the wrong impression about this.

  35. Bob Levine says:

    @Eric

    “The statement, “string theory does make predictions: it predicts supersymmetry, and this will be tested at the LHC” is technically correct. It does predict supersymmetry and this can be tested at the LHC, so I really don’t see your problem. You seem to be incorrectly interpreting this statement as saying that string theory predicts that supersymmetry should be observed at the LHC. If string theory is correct, then supersymmetry might be observed at the LHC, which is much different than saying that it predicts that it should be seen.”
    ———————————————
    I really *don’t* think so, Eric. Putting an hypothesis in an experimental situation where in principle its *in*validity cannot be tested—where it can be confirmed if it’s true, but not ruled out under any of the experimental protocols in question—is not what most of us understand as a ‘test’ of that hypothesis. It’s precisely this sort of disingenuousness that makes statements like Greene’s so suspect. If the lab conditions involved don’t make it possible to disconfirm, please *don’t* pretend you’re “testing” the proposal. And note also that it doesn’t help that Greene said, not ‘can/might be tested’ as per your gloss, but *will* be tested.

  36. Eric says:

    Dear Bob Levine,

    As in Peter’s case, I believe that you are misinterpreting Brian Greene’s statement, which has two points:

    1) String theory predicts supersymmetry
    2) Supersymmetry will be tested at the LHC.

    Each point separately is completely correct. However, you are combining these two points into a single point claiming that string theory will be tested at the LHC. This does not follow logically.

    As I clearly stated, the observation or non-observation of SUSY at LHC does not prove or disprove string theory. However, the observation of SUSY would, in fact, provide experimental support for string theory. This is all that Brian Greene is saying, nothing more, nothing less.

  37. Bob Levine says:

    No, Eric, I’m misinterpreting nothing. I was not talking about string theory at all, and I wonder why you thought I was. The defense of SUSY against its no-show at the LHC is, as you yourself have expressed it, that the energy regime of the breaking scale may be higher than what can be tested at the LHC, so that nothing that happens at the LHC can disprove SUSY; all that can happen at the LHC is that observations might confirm SUSY. So in what sense will SUSY actually be *tested*?? And that’s the problem with both what Greene says and what you say: string theory or no string theory, Greene is making an unjustifiable claim when he says that ‘this ([i.e. supersymmetry] will be tested at the LHC’, and you are making the same unjustifiable claim in defending his statement. An experiment which cannot in principle exclude a particular family of hypothesis can in no sense be said to *test* that hypothesis. Why is this conclusion even slightly contentious?

  38. EDR says:

    Dear Bob Levine and Eric,

    I agree with Bob’s criticism that the most natural reading of Brian Greene’s statement is misleading.

    This does, however, raise the question of how best to make a brief statement that suggests something more like: “If the LHC were to find evidence supporting supersymmetry, this would give a significant (though utterly inconclusive) measure of support to string theory.”

    The word ‘test’ is misleading in Greene’s context. What word or phrase would be better?

  39. Eric says:

    Dear Bob,

    What is being tested at the LHC is low-energy supersymmetry. More specifically, the theory that low-energy SUSY solves the hierarchy problem, provides the dark matter, and allows the gauge couplings to be unified is what is being tested. Yes, the scale of SUSY can be pushed higher if the superpartners are not observed at the LHC. However, in this case, SUSY cannot solve the above problems.

  40. Bernhard says:

    Eric,

    The statement Greene should have made is that SUSY is a testable theory and it will be tested at the LHC. Discovering SUSY would be supportive of string theory but in no way a test of it since of string theory is not a testable theory. Not finding SUSY or not finding anything at the LHC would not contradict string theory. You expect people to consider the two statements of Greene separately but for crying out loud this is the definition of a misleading way of arguing even if it were to agree with you that it is logically correct. Mind you also that even some physicists not very much into SUSY or strings might get the wrong idea, what to say the layman, which is Greene´s target.

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