Supersymmetry: The Higgs boson’s flexible friend

This post is also on The Guardian. See also Chapter 3.5 of Smashing Physics.

Next week I am giving a talk a the SUSY 2010 conference in Bonn.

It is a bit weird that there have been seventeen of these annual SUSY (for “SUperSYmmetry”), meetings, even though there is as yet no experimental evidence for SUSY. Perhaps it’s excusable. SUSY is still the best way I’m aware of to improve the Standard Model of particle physics.

To me the three biggest arguments in its favour are: One, it plugs an important hole in the theory. Two, it sort-of-predicts Dark Matter. Three, it looks nice.

Something looking nice in Bonn.

The first is to do with why the Higgs boson is not millions of times heavier than it is. Given we don’t know whether there is a Higgs yet, that’s a pretty forward-looking concern, but it is a real worry for the credibility of the theory. Basically without it, the Standard Model looks like a coincidence on the level of one in ten-thousand-million-million (1016). This is 100 times less likely than winning the lottery jackpot two weeks running if you buy a single ticket each week. SUSY introduces some quantum cancellations which make the Higgs mass much more stable, and therefore plausible. Still, maybe the universe got lucky. Some string theorists might say we should be glad it’s not one in 10500.

The second is the most compelling to me, since astronomical observations tell us there is probably some Dark Matter out there (or else we really do not understand gravity) and many SUSY models predict a particle which would be an ideal candidate for Dark Matter. It may be right behind you. When two different branches of science have problems which seem to converge on the same solution, look out for progress.

The third point is arguable and I may argue it later, but not now.

Another feature of SUSY is its flexibility. It can appear in many different guises in an experiment, to the extent that almost any weird event we see could (and will, I bet you) be interpreted as a “hint of SUSY”.

For example, a big part of my doctoral thesis involved simulating a SUSY process which we might have seen at the electron-proton collider, HERA. When you whack protons and electrons together, one thing which might happen is that the quarks in the proton stick to the electron. This would be a “leptoquark” (because electrons are leptons) and would be a sign of the unification of the strong, weak and electromagentic interactions, so-called “Grand Unification”. Very exciting stuff.

Just before we switched on, JoAnne Hewitt realised that the signature of a leptoquark also looked like a particular form of SUSY. Herbi Dreiner, then a postdoc at Oxford (and now organiser of SUSY2010) had realised that if so, there would other ways it could decay, and he calculated them.

I remember his calculation being given me on a napkin, but my memory may be embellishing here. Anyway, I wrote a program predicting how the results would look in our detector, so we could search for them.

Sadly they never showed up, though we did have a bit of a false alarm at one point.

Not-so-coincidentally, SUSY is one of the things we might also find at the LHC. In fact I have even written a couple of papers on some possible signatures. (Which is why I am talking at SUSY10). Basically I had a new experimental technique, and was looking for applications. SUSY provides some.

This flexibility makes SUSY a good test-case for experimentalists to make sure we aren’t missing anything. If we are alert to all possible SUSY processes, we are alert to a very wide range of weird stuff.

However, when weird stuff doesn’t show up, as so far it has not, that unfortunately does not disprove SUSY, it just rules out a given subset of SUSY models. This can be frustrating.

Still, to its credit, if there is no low mass Higgs, SUSY loses much of its attraction. It would not quite be ruled out, but it would certainly be relegated down the ranks of speculative theories. Conversely, if we do find a Higgs, the search for SUSY will become much more compelling.

Meanwhile, I had better write my talk.


About Jon Butterworth

UCL Physics prof, works on LHC, writes (books, Cosmic Shambles and elsewhere). Citizen of England, UK, Europe & Nowhere, apparently.
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9 Responses to Supersymmetry: The Higgs boson’s flexible friend

  1. Pingback: Europe by Physics and Train « Life and Physics

  2. yearzerowriters says:

    Good luck. I came here completely by accident because we had a spurt of through traffic from this post yesterday (we are a group of experimental writers who earlier in the year put together an anthology in priase of the Higgs Boson ). Glad I did, though, as it’s fascinating stuff (which is why we wanted to put the anthology together – to celebrate the art/science overlap – we have a reading night in Art jericho, Oxford, this Thursday on the same theme).

    Butting in as an amateur (and from the wrong side of the sticks – my degree is philosophy & theology, my teaching experience the philosophy of science – you must get sick of us ), I’m intrigued by what you say about Wheen (he gets around, doesn’t he? I remember his biography of Marx a whike back) and science being incremental whereas religion moves in leaps. How would you see scientific paradigm shifts fitting this model? Is it a question of an evidential tipping point, where the falsification evidence against the existing paradigm builds to such an extent that a new paradigm is required? If so, is this really different at a phenomenological level from the way that religions evolve? Is it not more that the nature of the incremental evidence is different in each case?


    • Hiya,

      I think incremental here is being used more in the sense of “cumulative”. Actually cumulative would have been a better word (blame Wheen 🙂

      In the spirit of the Gluckman quote on my front page, I guess.

      So the point is that there is a direction of progress. When something is discovered via a repeatable experiment, it is known in the the sense that future revisions of knowledge must somehow incorporate it. Such progress can occur both in small increments and in major leaps like those you describe, in fact.

      For bodies of study and belief not based on the scientific method, this cumulative progress is not obvious, revisions can throw away the entirety of previous “knowledge”. Which is not to say they are worthless, but they are different.

  3. Vicus Scurra says:

    I am a qualified agnophysicist (I know that that is not etymologically correct, but it is the scientific equivalent of agnostic). I spend a great deal of my precious time ridiculing the posturings of your colleagues (but mean no harm by it), having failed, many years ago, to make sense of the ramblings of Mr Sutton in what would now be sixth grade physics.
    I like your “making it up as I go along” comment, and am intrigued by “it plugs an important hole in the theory”. From my perspective “dark matter” and “dark energy” and good old “Higgs Boson” are names for stuff that we hypothesise in order to make sense of the universe as we perceive it. Others call this stuff “God”. What’s the difference?
    If I have upset you by this profound lack of respect, please feel free to visit my blog and ridicule it. That is what it is there for.

    • Hello. Of course I’m not upset!

      It’s true that “God” or the supernatural in general is often used to plug gaps in our knowledge. I think the difference is the framework, in that scientific knowledge, while always provisional, is incremental. (Francis Wheen put this very well in a book I happen to be re-reading right now).

      So dark matter, dark energy, SUSY or even the Higgs may turn out to be the wrong inventions to explain the current problems with our theories; but they are heavily constrained and motivated by the data we have, and they are also susceptible to experimental test. And if we find (for example) that there is no Higgs, it means the “Standard Model” is wrong, but it does not invalidate all the previous understanding of particle physics – it means we need a new, better theory, which still has to contain the predictive power of the old one for current measurements, but must extend that predictive power to LHC energies and above in a different way to the Standard Model.

  4. Luboš Motl says:

    Dear Prof Butterworth, an interesting text. Don’t you want this – and/or future texts of your of a similar kind – to be reposted on, enhancing the exposure of the comments by a factor of 50 (according to Thanks, LM

  5. Whatsamatta_u says:

    Please. No more formulae on cocktail napkins, for the following reasons:
    1) You write a formula on the napkin, and later, you sneeze into it
    2) Your companion writes the formula on the napkin, then gets run over by a car, and you sneeze into it.
    3) If the formula is no longer legible, research can be set back years.
    4) If the formula is the next E=mc^2, your snot-filled napkin will be on display in a museum for all posterity

    On the other hand, snot could very well be the model for dark matter, and the sneeze dark energy. But all the same, write down the formula elsewhere.

    • Fair point. It may in fact have been the back of an envelope. And it definitely wasn’t a cocktail napkin. More likely a baked-potato-beans-cheese-and-HP-sauce napkin from the Oxford Physics canteen. Herbi may remember, I will ask him next week.

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