What’s the Status of the LHC Search for Supersymmetry?

It’s been quite a while (for good reason, as you’ll see) since I gave you a status update on the search for supersymmetry, one of several speculative ideas for what might lie beyond the known particles and forces.  Specifically, supersymmetry is one option (the most popular and most reviled, perhaps, but hardly the only one) for what might resolve the so-called “naturalness” puzzle, closely related to the “hierarchy problem” — Why is gravity so vastly weaker than the other forces? Why is the Higgs particle‘s mass so small compared to the mass of the lightest possible black hole?

Click here to read more about the current situation…

13 responses to “What’s the Status of the LHC Search for Supersymmetry?

  1. “Gravity weaker than…..”:

    Doesn’t gravity work the other way around?

    • What do you mean? Gravity is by far the weakest known elementary force — you can lift you arm easily with electromagnetic forces despite the gravitational pull of the entire earth. Am I not understanding your question?

      • I just wonder whether there is a connection betwween gravity getting weaker when distance grows whereas f.i. electromagnetic interaction force gets stronger when distance grows.

        • You’re confused, for some reason; they both become weaker with distance, like 1/(distance)^2. Coulomb’s law, versus Newton’s law.

          No forces get stronger with distance. A confining force is the best you can have, and that becomes constant with distance, like the tension on a string.

          • As I understand it the charges of electrons in higher orbits are higher than the charges of electrons in lower orbits.

          • Martin you are very confused. Electrons all carry a single negative charge. In atoms electrons are arranged in atomic orbits which are termed s, p d and ultimately f. Irrespective of the atomic orbital each electron can only have a single negative charge.

  2. 1. One of the most puzzling of the experimental SUSY exclusions to me is the very modest (excluded at ca. 90-105 GeV or less) exclusions for the four extra SUSY Higgs bosons if the SM-like one at 125 GeV is H, then h, A, H+, H-, H++, and H–, or if the SM-like one at 125 GeV is h then H, A, H+, H-, H++, H–. Is the problem that there is not much agreement on the properties that these extra SUSY Higgs bosons would have?

    Why doesn’t the failure to find a signal of a SM-Higgs boson at 0-124 GeV and 127 GeV-600 GeV also operate as an exclusion of one or more of these extra Higgs bosons? Why should it be so hard to find a charged Higgs boson which I would think would have a very distinctive signature?

    Tightening exclusion ranges on extra SUSY Higgs bosons would seem as if they would constrain SUSY parameter space a great deal.

    2. In the same vein, some SUSY proponents argue that the LSP or the small neutral scalar SUSY Higgs boson can have a mass less than the 125 GeV of the Higgs boson, notwithstanding LHC exclusions at much higher energies. How credible are these claims and what assumptions do they require?

    3. I have heard others claim that LHC much more clearly excludes R-parity conserving SUSY than it does R-parity violating SUSY, do you agree?

    4. Does your analysis factor in considerations like limits on SUSY from the low value of the Electric Dipole Moment of the electron that Jester called attention to last month? http://resonaances.blogspot.com/2013/11/electric-dipole-moments-and-new-physics.html

    5. Are there other non-LHC experiments you see as having an important impact on the available SUSY parameter space?

    • 1) This is a detailed question. [You’re overcounting the number: there are h, H, A, H+, H-; there is no H++ or H– required.] We expect the other Higgs bosons to be heavy, perhaps quite heavy, given how STandard Model-like is the first one we’ve found. Heavy means 200-1000 GeV. Heavy charged Higgs bosons do not have distinctive signatures; there are large backgrounds and the production rate is small. In fact finding the neutral ones may be much easier. And unfortunately the restrictions on supersymmetry of not finding the other Higgs bosons yet are not very strong. It is possible they will not be detectable at the LHC at all, or at least not for a long time yet.

      2) Very detailed, too much for this website. What they say is possible, and very credible if nature has more neutral Higgs bosons than the minimal number (i.e. if in addition to h, H, A there are more neutral ones).

      3) What you learn is that no one reads my papers. :-) As I pointed out in 2006, R-parity conserving models with hidden valleys attached to them would end up, in some cases, no more excluded than R-parity violating models. [This is especially true in the very clever set of examples called “Stealth Supersymmetry”, invented by Jiji Fan, Matt Reece and Josh Ruderman.] Indeed we used this fact in the studies that we did in our recent paper, see Wednesday’s post.

      4) We don’t factor these measurements in because it is easy to change the electron dipole moments without changing the LHC signatures, and vice versa. They’re orthogonal pieces of information, and our aim was to obtain general results, not ones that would depend on exactly how you arranged the particles at higher energy (or weaker coupling) that the LHC can’t yet measure. In other words, our paper would be useless if we tried to do this — it would become an extremely complicated morass without any clear message.

      5) Many… too many to list, or rather, I don’t want to embarrass myself or annoy my colleagues by forgetting one. However, the problem is that you can’t extract simple lessons from them about supersymmetry as a whole. Non-LHC experiments are very, very important in ruling out specific classes of variants of supersymmetry. They could turn out to be essential in (a) discovering the Standard Model is wrong, or (b) diagnosing a discovery of new particles made by the LHC. But they are almost useless in *ruling out supersymmetry*. (This is the same issue with the LHCb measurement of B_s mesons decaying to muon-antimuon pairs.) With such experiments you can make discoveries or rule out specific possibilities, but you can almost never attack the general case. The point of our paper is that when you think about it in the right way, you can now make some almost completely general statements about what we do and don’t know about the gluino in a natural supersymmetric model. To my knowledge this has never been done before.

  3. I understand the process your going through with regard to the LHC, but I am wondering if from another perspective the issue of symmetry is still ripe with regard to other research areas?

    “The ideas that arose in coming to terms with the classic superfluids are ripe for generalization, and have proved extremely fertile. By focusing on symmetry and its breaking, we can generate questions and answers in seemingly far removed fields (as we’ve already exemplified), and suggest new phenomena.” http://frankwilczek.com/2013/superfluidSymmetryBreaking.pdf

    • Using exact or approximate symmetries as a way of recognizing simplicity in complex situations proves very useful in many contexts, from first-year undergraduate physics to the most up-to-date research.

  4. Could there be an even lighter Higgs boson than the one they found?

    Is the Higgs a “real” particle, in the same definition as the one we can “see”, or is it a process in which particles get created? A transition between nothingness (zero point energy) and resonances.

    I suppose you can rephrase the question by how does the Higgs mechanism tie in with supersymmetry or symmetry breaking?

    We don’t know what a black hole is and hence we don’t know how many different types of black holes exist and/or can be created. Can be due to a collapsing stars but could it also begin by creating WIMPs? A runaway reaction of the creation of a space consisting of WIMPs and growing very rapidly cancelling particles as it grows. Could WIMPs be antiparticles of Higgs bosons? I am not trying to contradict myself by inferring the Higgs as real, but rather, in order to maintain supersymmetry a state exist to counter the creation of real particles.

    Can the LHC create WIMPs?

  5. @ Dave

    Your comment is not to the point. The question is whether or not the electron’s charge is constant irrespective of its orbit, its distance to the nucleus.

    BTW, I have the same question with regard to an electron’s energy (mass).