LHC results put supersymmetry theory ‘on the spot’

The HEP theory community is atwitter over a BBC News story LHC results put supersymmetry theory ‘on the spot’ that reports from the Lepton-Photon 2011 conference in Mumbai, where more null results relevant to supersymmetry were reported. According to the story:

Results from the Large Hadron Collider (LHC) have all but killed the simplest version of an enticing theory of sub-atomic physics.

Researchers failed to find evidence of so-called “supersymmetric” particles, which many physicists had hoped would plug holes in the current theory.

Theorists working in the field have told BBC News that they may have to come up with a completely new idea.

Joe Lykken, an organizer of the SUSY11 conference about to start at Fermilab, is getting worried:

“There’s a certain amount of worry that’s creeping into our discussions,” he told BBC News.

The worry is that the basic idea of supersymmetry might be wrong.

“It’s a beautiful idea. It explains dark matter, it explains the Higgs boson, it explains some aspects of cosmology; but that doesn’t mean it’s right.

“It could be that this whole framework has some fundamental flaws and we have to start over again and figure out a new direction,” he said.

On Twitter, there’s Carlo Rovelli gloating here, Matt Strassler (here and here) and Lisa Randall (here) claiming all is not lost. In an exchange here, Strassler notes that he’s fighting to prevent the risk of “no money for your research”. It’s unclear if he’s referring to funding for the LHC experiments or for SUSY theory. There is a real long-term danger to HEP experimental funding once the public realizes that they’re not getting the extra dimensions some have promised them, but the time to fight that risk was the many years during which hype about the LHC was rampant.

Both Strassler and Kane now seem to attach great importance to the point that, in some SUSY variants, gluino mass bounds are lower than the 1 TeV of the most popular models, more like 500 GeV. Kane goes so far as to claim that the gluino will be found, at masses below 1 TeV:

The current limit on gluino masses is not above 500 GeV. Whether the squarks are indeed so heavy is not the issue, the point is that if they are the limits on gluino masses are smaller than is often stated. I and others expect this decay to tops and bottoms is the signature by which gluinos will be found, with masses well below a TeV.

Presumably LHC searches are underway for signatures of gluinos in this mass range in these versions of SUSY. I’d be very curious to hear what the status of those searches is. If they come up negative, will SUSY proponents finally give up? New results relevant to SUSY are appearing rapidly, see the latest from CMS here and here.

For some historical perspective, something I ran across recently was a 1993 New York Times report 315 Physicists Report Failure In Search for Supersymmetry, which described null results from early days of the Tevatron. One very funny thing about the article is that much of its emphasis was on the unwieldy nature of the CDF detector, with its $65 million budget and huge number of 315 physicists.

Update: SUSY11 opens tomorrow with a talk by Murayama that incorporates the BBC News story and describes evidence against superpartners as “impressive, worrisome, but not quite there yet”. No indication of when it will get there. The title of the talk: Why do SUSY in 2011?

Update: Quite interesting reading is Michael Peskin’s summary talk at Lepton Photon. On the topic of this posting, he writes:

Before the start of LHC, I expected early discovery of supersymmetry in the jets+MET signature. Many other theorists also had this belief. But, it was not correct.

and he explains why this was (large amount of fine-tuning required if superpartner masses are even as large as 1 TeV). He also explains possible ways to construct SUSY models that evade current experimental bounds while keeping superpartner masses relevant to the fine-tuning problem from getting much too large.

This week at CERN there’s a workshop on Implications of LHC results for TeV-scale physics, which should have many interesting talks.

Update: Yet another technical talk about the state of SUSY searches that begins by reproducing the BBC story is today’s talk at CERN by John Ellis. Ellis gives an overview of SUSY fits. The regions identified by these (pre-LHC) as the most likely place for SUSY to show up have in many cases now been ruled out. With the latest LHC data, the “most likely” region moves out to higher and higher masses, with less and less of a good fit. Ellis concludes:

LHC data putting pressure on popular models.

Update: Another review of the SUSY situation is here (from the Physics in Collision conference). A quote from Altarelli:

It is not time to desperate yet… but maybe it is time for depression already.”

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70 Responses to LHC results put supersymmetry theory ‘on the spot’

  1. Peter Woit says:


    They switch to heavy ions in early November. After a shutdown, early next year it’s back to protons, with an energy increase possible depending on the results of measurements made during the shutdown.

    In principle the data gathered by the two experiments is independent, so it should make sense to combine it and improve the statistical significance of any signal. As far as I know, they have a mechanism in place to do this kind of combination, and I don’t see why they wouldn’t do it, after each experiment has independently reported its own combined result. I have no idea what the timing of this all will be. End of year? Earlier if one of the experiments feels they have a convincing signal and wants to announce it?

  2. Paolo Valtancoli says:

    I remember that Hawking doesn’t believe to the Higgs boson, but believes in supersymmetry and M-Theory. I think that the idea of supersymmetry will survive for many years to come even though LHC finds absolutely null results.

  3. Peter Woit says:

    The latest projections about the Higgs are consistent with my comments above, and given in detail here:


  4. chris bolger says:

    Can the W+, W- and Z be considered as supersymmetric to the e+, e- and neutrino. If not, why not?

  5. Eric says:


    The W’s and Z are in the adjoint representation of SU(2), while the electrons and neutrinos are in the fundamental representation. Supersymmetry does not act on the group representations, and so there is no way for the W’s and Z’s to be transformed into e’s and neutrinos by supersymmetric transformations.

  6. null says:

    “On the topic of this posting, he writes:

    Before the start of LHC, I expected early discovery of supersymmetry in the jets+MET signature. Many other theorists also had this belief. But, it was not correct.

    and he explains why this was (large amount of fine-tuning required if superpartner masses are even as large as 1 TeV). He also explains possible ways to construct SUSY models that evade current experimental bounds while keeping superpartner masses relevant to the fine-tuning problem from getting much too large.”

    What is the upper bound for SUSY masses while keeping superpartner masses relevant to the fine-tuning problem , and is it within LHC full design energy 14TEV, or does it evade it?

  7. Peter Woit says:


    The problem is that there is no well-defined point at which the necessary fine-tuning is “too much”. 1%? .1%, .01%???

    Many people did argue before the LHC was turned on that the LEP and Tevatron bounds on superpartners (and bounds on the Higgs mass) already forced a degree of fine-tuning that made supersymmetry unlikely. In simplified terms, the scale of electroweak symmetry breaking is of order 100 GeV, and if supersymmetry breaking is responsible for this, it should be of the same order, whereas this is ruled out by Tevatron/LEP bounds.

    The problem for SUSY enthusiasts is that bounds are now moving up to 1 TeV and above. They have to either give up on the fine-tuning argument, or say that 1 TeV is not a problem. Once you say 1 TeV is not a problem, there’s no reason 2, 3, 5 TeV should be a problem, so it really doesn’t matter how much the LHC bounds get pushed up.

    The argument Strassler and some others are trying to make is a bit different. They argue that until you rule out all the different kinds of signatures (not just the simplest ones) you can get from different patterns of masses, you really haven’t ruled out SUSY below 1 TeV.

  8. Bernhard says:

    Yes, some people are definitely giving up on the fine-tuning problem as SUSY motivation:


  9. Eric says:


    Low-energy supersymmetry was formulated to stabilize the Higgs mass against radiative corrections, rather to provide an explanation of EWSB as you state above. Thus, there is absolutely no reason to expect that the superparner masses should be the same as the electroweak scale ~100 GeV. In order to make the Higgs radiatively stable, the superpartners only need to be of the order of a few TeV, not 100 GeV. When you quote this number, it gives people the wrong impression about the current degree of fine-tuning necessary for supersymmetry to solve the hierarchy problem.

  10. Thanks for the clarification. I must defer to your better opinion on the matter. I suppose null results for luminiferous aether in 1887 did lead to a revolution in physics, although it all seems a little discouraging at the moment.

  11. Marcus says:

    I’m not a physicist; I’m a professor of philosophy, and all I know about this stuff is the (considerable) amount of pop physics I’ve read, blogs like this one, and a tiny bit of online self-education. So, having drawn attention to my ignorance, I have a simple conceptual question that has been bugging me. The question is this: how is it even coherent to say (1) that the SM Higgs is supposed to give other particles their mass, and then say that (2) the SM gives no account of gravity (which is true), when we also know that (3) an object’s mass is what generates its gravitational field. This looks plainly incoherent. If the SM cannot account for gravity, how COULD there be a SM Higgs (given that gravity is a matter of something’s mass)? I’m sure I’m making a mistake somewhere, but where?

  12. SpearMarktheSecond says:

    Marcus… the Higgs gives certain fundamental particles their mass. But there are other sources of mass… most of the mass of our kind of matter is caused by energy in the gluon field between the quarks in neutrons and protons, which is not the Higgs at all. However, the masses of neutrons and protons are not quite as fundamental as the masses of neutrinos, or electrons, or quarks (the fermions), and it has been the fundamental questions that have attracted people.

    Classical gravity doesn’t care what the origin of the mass is… given some mass of any origin classical gravity can take it from there.

    Of course everyone would like a complete unified quantum theory of it all, but we don’t have that yet…. or perhaps we have too many and don’t know which to pick . In any case it is unsettled.

    On the no lose theorem… here is an old paper in favor of the SSC and against a center of mass energy lower than 20 TeV…


  13. Florian says:

    I don’t particularly like SpearMarktheSecond’s explanation to Marcus’s question, so I offer another one.

    Mass is not only associated to gravitation. Mass also measures how inert a body is. The masses one talks about in the context of the Standard Model refer to this understanding of mass.

    Well, actually the masses in the SM are just parameters in the theory. We call them masses, because in some experiments particles appear to be inert (e.g. electrons in a synchrotron). Now if you want to formulate the SM in a certain way (gauge invariant), it seem to be necessary to introduce one more particle – the Higgs boson. (Otherwise putting masses for some particles in by hand would destroy gauge invariance.)

  14. Igor Khavkine says:

    @Marcus: There is a hidden equivocation in your logic on the term “mass”. Physicists can easily spot the change in the meaning of that word from context, as partially explained by SpearMarktheSecond.

    In general, mass, energy and momentum are distinct but related concepts and quantities. When used colloquially, the term “mass” may stand for any one or combination of them. Here are some different context where it can appear.

    Inertial mass is an empirical notion which can be determined from experiments comparing the force acting on on object and its acceleration. Inertial mass is combined in a specific with an objects energy and momentum into an energy momentum tensor (which just reduces to gravitational mass in Newtonian gravity), which is entirely responsible for the object’s interaction with gravity in General Relativity. For a composite object, its inertial mass is determined in a specific way from the energies, momenta and inertial masses of its constituents. For elementary (non-composite) particles, the inertial masses are determined in a specific way by parameters that enter into the mathematical formulation of the Standard Model. These parameters can be roughly split into two classes: the particle masses and the interaction strengths (aka coupling constants). Oddly enough, the Standard Model sets all particle masses (except for the Higgs boson) to zero. This means that the inertial masses of the elementary particles that we observe are entirely due to the strength of their interaction with the Higgs boson. In particular if a certain property of the Higgs boson known as its vacuum expectation value increases by a factor of 10, the inertial masses of all other elementary particles universally increase by 10 as well.

    It is in the following sense that the Higgs boson gives other particles their masses: the strength of the interaction of an elementary particle with the Higgs boson determines its inertial mass. Since inertial mass does not necessarily involve gravity in its definition or measurement, the points (1) and (3) in your reasoning are actually logically disconnected.

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  16. Anon says:

    Could someone explain to this naive reader what is keeping us from doing these kinds of searches with high energy cosmic rays, which commonly have much higher energies than those achievable at the LHC? Not enough supply?

  17. Peter Woit says:


    Enough about mass, this isn’t a forum for general physics discussion, I can’t moderate such a thing. As general advice to anyone trying to learn more about basic topics in physics, internet comment sections are not a good place for this. You’re much better off getting hold of a real book, with equations, where someone competent has put a lot of effort into writing something long, careful, with equations. This is what you need to understand a basic concept like mass.


    For short questions like yours, you can get the answer from a comment section, although I really wish people would stick to the topic of the posting. Again, a general discussion area is too hard to moderate. In this case though, the simple answer is luminosity. At the LHC you have many high energy collisions every nanosecond and you may need a year’s data to get what you want. If you instrument some area of the earth or space and wait for LHC energy collisions, they will be very rare events.

  18. Bernhard says:

    Seems the focus for the Higgs mass searches are now between 114-145 GeV by all accounts, but Bill Murray´s slide 6 points to the possibility that in fact its mas could be say 600 GeV. I thought this was almost excluded by electroweak measurements. How much not excluded is this > 460 GeV region? And of course, what does it mean for SUSY? Are there any SUSY models floating around with such a heavy Higgs?

  19. Eric says:


    A superheavy Higgs (m> 600 GeV) would be natural in a four-generation SUSY model, since in such a case the Higgs receives large radiative corrections.

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