Of Particular Significance

An LHC Workshop in London

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 09/30/2011

For me, one of the great pleasures of scientific research is the small, focused “workshop”, where a few scientists (typically 20 — 40 faculty, postdoctoral researches and students) assemble for a day or two to discuss a particular topic in detail. Presentations are typically short and often quite informal, and there’s lots of time for discussion built in to the schedule. The best workshops, of course, are those where the quality of the science and the knowledge, experience and skill of the participants is exceptional. I was fortunate to enjoy such a workshop yesterday at Imperial College in London, one of Britain’s finest scientific institutions.  About half the participants were experimentalists from the CMS experiment at the Large Hadron Collider (LHC) and the other half theorists like myself (one of whom is also on the ATLAS experiment at the LHC.)

Another great pleasure in doing science, at least in my field, is its international nature. The participants from yesterday’s workshop included scientists from at least seven countries and three continents, many of whom are now working in a country that is not their native land. Add to this diversity of cultures, appearances and accents some lively personalities, good senses of humor, and high quality science, and you have the ingredients for a very serious workshop that is a very serious form of fun, followed by much less serious fun when the workshop is over and everyone who can stick around goes out to a pub, a restaurant, and then another pub.

The workshop was focused on the searches at the CMS experiment for supersymmetry (a speculative but popular suggestion for what might lie beyond the known particles, and might be the solution to the hierarchy problem.) I should add that I haven’t written nearly enough about other possible solutions to the hierarchy problem, mainly for lack of time; they will come eventually.  I’ve focused on it because it’s been in the news at lot, because of various overstatements by physicists that have shown up on the blogs and various places in the media, saying that this summer’s results from the Large Hadron Collider show that supersymmetry is basically ruled out.   So far, every expert in the subject I have spoken to agrees with me (and I would consider myself only a moderate expert) that this is simply not the case. There are huge loopholes (learn about a few of them here) in the claim that “supersymmetry is virtually ruled out” that you could drive a supersymmetric truck through, and there’s lots of work left to do if we are to assure ourselves that neither supersymmetry, nor anything like it, is in LHC data.

Discussions at yesterday’s workshop were focused on understanding what has and hasn’t yet been looked for in the search for supersymmetry — where are the largest and most compelling loopholes, and how do we start to close them?  Here’s the problem: we have a vast continent of variants of supersymmetry (and other models that might give similar experimental signals) that we have to search for; we have only a few thousand experimentalists who can form a few dozen search parties; so we need to know: what are the biggest and most fertile unexplored regions, and what are the most efficient search strategies?

The workshop opened with a couple of talks by two experimentalists from CMS, the first addressing the question “what have we done so far?” and the second “ what are the issues/concerns for the future?”. The rest of the short talks came from theorists, with very diverse and complementary points of view.   I personally found the discussion and exchange of information especially profitable. The challenge now is to convert this exchange of information into a proposed strategy. That requires follow-up and a certain amount of organization, not a simple matter when everyone is so incredibly busy — and this will be my focus for today, as I remain in London.

Needless to say there was some conversation after the workshop about the OPERA experiment and its claim of early-arrival neutrinos.   The level of skepticism is extremely high.  I’ll post about that separately.

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5 Responses

  1. I dont know why you say that, I have a good track record predicting that the LHC results were not as good as they looked in July – before it became clear in August, as well as questioning the results of Opera on your blog before everyone else joined in. I think the issue with supersymmetry is not whether it has been ruled out – it is likely it will never be – but whether it is relevant. The latest results from the LHC are a serious blow to supersymmetry in that aspect. They indicate that, unlike what had been hoped for, supersymmetry can not explain EW unification.

  2. The first line above should read ‘objective’ not ‘subjective’ – its a pity I can’t edit this thing.

    I should like to mention one thing in connection with what I said above. The main problem plaguing all major theories devised since the seventies is a plethora of extra particles which these theories predict in addition to those that are actually known to exist. This applies in equal measure to variations of technicolor, supersymmetry, and superstrings. This is actually indicative of the excessive numbers of degrees of freedom present in those systems. It is relatively easy to fit an experiment to a theory with the number of degrees of freedom exceeding the number present in the experiment – but the fact that that’s all you have done is reflected in the extra degree’s of freedom left over – as such the extra particles should be welcomed not loathed. Nature has been quite sparse in the number of degrees of freedom it uses. So I think we will know we have come up with the right unification theory when using the least parameters we predict the universe and no more.

    1. People used this argument in the past to predict there would be no neutral currents (i.e. no Z particle) and were wrong. They used it to predict that there would be no neutrino masses, and were wrong. Nobody expected the muon. In fact, back in the 1920s there was no reason to expect the neutron. And in the 1800’s, someone taking your point of view would have failed to predict all the as-yet unknown elements in the periodic table. I don’t think history agrees that taking a minimalist approach is always a good idea. Sometimes it is, sometimes it is not.

  3. People making a living in the field are not necessarily subjective when it comes to making a judgement of when its time to put supersymmetry on the back burner. This is aggrevated by the fact that there are no real alternatives to turn to – this is why theres so much interest in Opera – though most people dont really believe it. The trouble is that physics has been in the doledrums as far as successful new ideas are concerned since the early severnties, and the likely imminent failure of the Higgs scenario, which dates back from the sixties, shows that even that is too optimistic. It is beginning to look like , gravity and QFT are just not unifying (without suppersymmetry and a plethora of particles) and with the Higgs in trouble, even what we have thought we had unified appears to be coming apart. I suspect the two failures are not unrelated.

    To help demonstrate how difficult the situation is, using something familiar to those acquainted with rudimentary quantum mechanics, consider the early 20’th century before quantum mechanics was invented. One knew light is emitted in quanta, Einstein (a subsequent opponent of QM) even proposed that the electric field itself is quantized (photons), they also knew that the Rutherford model of the atom with electrons orbiting the nucleus conflicted with Maxwell’s theory that accelerating charges should radiate – so the planetary atom was unstable. Imagine experimental input then suddenly coming to an end, with scientists left for a century, just on the back of that, to explain atomic structure – no emission spectra, no Zeeman effect, no new particles, nothing else. One can imagine all sorts of mechanical and statistical systems being invented with ever more comlicated interactions – because that is all people knew, and the only things that had worked before. But nobody in their right mind would have come up with quantum mechanics, to wit, that below this world of order there is a huge lotery going on. Today the situation is that to do just one experiment, of predictive value perhaps even less than a simple Zeeman splitting measurement, one requires a world collaboration such as the LHC, using money that perhaps never again will be available if nothing is found. One can see the scale of the problem there.

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