# The Smell of SUSY

The implications of the failure to find SUSY at the LHC are beginning to sink into the particle physics community: the paradigm that dominated the subject for the past 30 years has collapsed in the face of experimental (non)-evidence, threatening to take down the life’s work of hundreds if not thousands of theorists. For some recent attempts to quantify what is going on, from some people with much more statistical expertise than me, see Philip Gibbs and Tommaso Dorigo. By now a significant number of SUSY analyses of the full 2011 dataset have been completed, with negative results. By the end of the year there will be more data, but just a factor of 2-3 more, at about 14% higher energy. To believe that these sorts of increases will turn no signal into a signal requires a willingness to engage in a rather large amount of wishful thinking. The 62% jump in 2014 to 6.5 TeV/beam is more significant, but it’s hard to see an argument for why this should do the trick, and the wait for these results will be discouragingly long, probably until 2015. How many SUSY enthusiasts will keep the faith?

A small number of theorists though still claim all is well, with one group producing a new paper claiming the full 5 inverse femtobarn results show Chanel No5 (fb^-1): The Sweet Fragrance of SUSY. Last year the same authors were claiming to detect Profumo di SUSY in the first inverse femtobarn, and argued that 5 times more data would be conclusive. To quantify the SUSY smells they are advertising, one can plot as a function of time their published predictions for the parameter $M_{1/2}$ which determines the gluino mass.

arXiv:1007.5100 455 GeV (“Golden Point”)
arXiv:1009.2981 455-481 GeV (“Golden Strip”)
arXiv:1111.0236 512 GeV (“Universe F-U2”)
arXiv:1111.4204 518 GeV (“Profumo di SUSY”)
arXiv:1203.1918 610 GeV (“Aroma of Stops and Gluinos”)
arXiv:1205.3052 708 GeV (“The Sweet Fragrance of SUSY”)

It’s rather easy to extrapolate to the future what these authors will be claiming the SUSY masses are, harder to extrapolate how they’ll be describing the smell. The rest of the particle physics community I suspect is already using very different terms for this.

Update: According to this report from Pheno 2012

As pointed out by Rahmat Rahmat (yes, that’s his name—in my notes I list him as Rahmat2) and Csaba Csaki, respectively from University of Mississippi and Cornell University, the LHC should have detected some signature of SUSY by now, especially if the MSSM is correct. As Csaki said, “SUSY is a wonderful woman who does not return my letters. It makes you wonder if she even exists!”

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### 19 Responses to The Smell of SUSY

1. Aaron Davies says:

Last year the same authors were claiming to detect Profumo di SUSY in the first inverse femtobarn

It’s the Profumo Affair!

2. rrtucci says:

Maybe you should have titled it:

3. Frank says:

Peter, some people are starting to play a well-known game with supersymmetry: whatever negative result comes in, they answer that it does not refute supersymmetry. This behavior begs the following question, which you know well enough from a similar field: is there any definite, testable prediction of supersymmetry at all? Or even more precisely: is there any definite, testable prediction of *broken* supersymmetry?

To interested people it seems that none of the concepts introduced by supersymmetry, from sparticles to super-gauge fields, has any evidence to back it up. This begs a second question: Why have people been so convinced about supersymmetry to start with?

4. Speculative says:

Frank,

1) Unlike String Theory, SUSY is certainly testable. The problem with discovering or ruling out SUSY is not its testability but its parameter space. That is there it will take a lot of experimental work to really rule it out. It is probably impossible to rule it out completely, rather if a large enough parameter space is ruled out theorists and experimentalists may just move on. Theories usually not outright disproven, but rather proven untenable.

2) SUSY is (or was) appealing because it seemed to solve so many problems at once. It makes working with the math nicer, it fixes the gauge coupling at higher energies (so they all converge at the hoped for GUT scale), and it gave possible candidates for Dark Matter. Of course this doesn’t matter if it doesn’t actually exist but the search for it is certainly not without merit.

My feelings coincide with Professor Strassler. We need to wait and see and not jump into any conclusions. Science is a slow process and there’s no need to rush it or jump to conclusions. That being said, the results coming out of the LHC aren’t encouraging, but you never know how things can change.

5. Hun Hunahpu, PhD says:

This accelerating increase in the gluino mass indicates that one of the hidden dimensions is rapidly decompactifying. My calculations indicate that the transition to a genuinely five-dimensional macroscopic world should occur a little over seven months from now.

6. don says:

I think both sides of the SUSY debate have jumped to conclusions too quickly. Those who worked on it believed it would be found soon after the LHC started up and now those who were skeptical of the idea believe SUSY is dead. What is happening now reminds me of the state of the Higgs search about nine months ago when nothing had been found yet and people were declaring the Higgs dead. SUSY might be right or it might be wrong, let’s wait until we have more data before we jump to conclusions. This search is, after all, one of the reasons the LHC was built, let’s let it do its job. And let us not forget this point: we will not have evidence of something until we have evidence of something. This is what science is all about: we have a problem, we come up with an explanation that attempts to solve the problem, then we test it.

7. Peter Woit says:

don,

I don’t think there’s much parallel to the Higgs case, where I don’t remember anyone declaring it dead, just some speculation about what it would mean if it were ruled out.

In the SM Higgs case the predictions are very solid, with one free parameter, so it has always been very clear exactly what is ruled out (some range of the one parameter at various confidence levels). For SUSY, there are vast numbers of parameters to describe even the simplest SUSY extension of the SM, and it will never be possible to say “SUSY is ruled out at X confidence level”. So, it’s worth getting clear on exactly what the case for SUSY is, what exactly you expect to see at the LHC if that case is valid, and exactly what the analyses show. I’d argue that pre-LHC the case for SUSY was weak, with many arguments for it leading to the conclusion that it should have already shown up. The only remaining hopes for those arguments required SUSY to show up early in the LHC data, and it didn’t. We’ve now seen quite a few analyses of the full 2011 data set, and there’s no good reason to believe the 2012 data set will make large increases in the exclusions already available. So, now is a good time to start drawing conclusions. You can try and argue to wait for 2015-6 and higher energies, but I don’t think there’s a good argument there, just an attempt to stall for a few more years.

8. don says:

I think I am being fair when I say that while SUSY may not be true it is at least a reasonable theory that very well could be true. I think it is also fair to say that we are nowhere close to having excluded over 95% of the possible reasonably likely iterations of SUSY. Let’s search and then draw conclusions after we have at least a year of full power LHC. It’s not as if we are wasting our time on a crackpot theory that has almost no chance of being correct or that we even have very many other sensible theories at this time that could possibly go beyond the Standard Model. Perhaps you will argue that we should move on now, cut our losses, and try to come up with something new. I’m all for alternatives to SUSY, but I also believe that we can multitask.

9. Peter Woit says:

don,

My point was more about what theorists should do, not what the LHC experiments should do. It’s long past the time that theorists should admit that things like the MSSM are a failed idea. I see no argument for waiting until 2015-6 for this.

As far as the LHC experiments are concerned, they certainly shouldn’t stop SUSY analyses, and in any case there’s no danger of that. It would however be a good idea for the people making decisions about which analyses to do (or how to design triggers) to have a realistic point of view about the prospects for SUSY, not an overhyped one.

10. Visitor says:

“As Csaki said, ‘SUSY is a wonderful woman who does not return my letters. It makes you wonder if she even exists!'”

Beware non-existent women! Heed the troubles of Paul Frampton, and let it be a cautionary tale for you!

11. neo says:

“My point was more about what theorists should do, not what the LHC experiments should do. It’s long past the time that theorists should admit that things like the MSSM are a failed idea. I see no argument for waiting until 2015-6 for this.

As far as the LHC experiments are concerned, they certainly shouldn’t stop SUSY analyses, and in any case there’s no danger of that. It would however be a good idea for the people making decisions about which analyses to do (or how to design triggers) to have a realistic point of view about the prospects for SUSY, not an overhyped one. ”

“long past the time that theorists should admit that things like the MSSM are a failed idea. I see no argument for waiting until 2015-6 for this”
PW,

How does the failure to find SUSY in 2011 data set @ 7TEV energies translate to not likely finding evidence for SUSY at 14TEV (or 13TEV)

do you think there will be new physics, such as SUSY, in a proposed future upgrade to a higher-energy LHC (“HE-LHC”) with about 16.5 TeV beam energy (33TEV)?

12. Peter Woit says:

neo,

The main argument for SUSY at LHC energies has always been that it would solve the hierarchy problem and stabilize the weak scale. The problem with this argument was always that if so, you should have already seen evidence for SUSY pre-LHC. One could argue though, that it was just beyond the pre-LHC range. That argument is now dead. I don’t see a good argument for expecting SUSY either at 13 TeV or 33 TeV. Hopefully the LHC will see something non-SM, which will justify building an HE-LHC to investigate. Otherwise, the main argument for the HE-LHC will just be to check the SM at higher energies. That would be enough for me, but it will make selling the machine harder.

13. neo says:

A certain string partisan, whose name I won’t mention, debated this with Tommaso Dorigo on his blog, that in his view, the situation is similar to the hunt for the Higgs – Higher energies + enough data takes time to collect and analyze, and there are many versions which have not been ruled out.

14. Peter Woit says:

neo,

The MSSM adds more than 100 parameters to the SM, you will always be able to find corners of parameter space that the LHC can’t rule out, or just push the SUSY breaking scale high enough. Some fraction of SUSY diehards will never give up on the idea, no matter what. If you look at Lubos’s long posting about this, it boils down to his accurate argument that if your prior probability is 99.99% that SUSY exists, the LHC exclusions don’t change your beliefs by much. Or, less technically, if you’re a fanatic, experimental evidence is pretty much irrelevant. Most people however are not fanatics, and opinions about SUSY in the mainstream are definitely changing substantially in response to the LHC results.

Interestingly, even Lubos doesn’t believe the “Smell of SUSY” argument of Nanopoulos et al., which is remarkable.

Why the SUSY search with its vast number of free parameters is just like the Higgs search, with its one parameter, escapes me.

15. neo says:

I didn’t mention the name yet you correctly guess. Haha. His claim “Your analogy with the Higgs allowed intervals is very appropriate. When we’re approaching a discovery, we’re inevitably able to eliminate increasingly large portions of the regions that were possibilities just a year ago. This just means we’re learning something about the details of the model. For Higgs, the discovery could actually take place well before the exclusions of the most of the parameter space because its signals are sharp as a function of the Higgs mass. But this didn’t occur. For SUSY, the signals are much more widespread as functions of the superpartner masses so we must clearly expect to exclude an even higher fraction of the parameter space before the discovery – at least one able to find out the masses of the new particles – can actually be made.”

In his opinion, the current LHC bounds only exclude a small fraction of the SUSY parameter space, MSSM and still resolve the hierarchy problem and stabilize the weak scale.

16. Peter Woit says:

neo,

In Lubos-land, it doesn’t matter how much parameter space the LHC rules out, or how much fine-tuning is required for the MSSM to “resolve the hierarchy problem and stabilize the weak scale”. 5 years from now when the LHC has gone to higher energies and luminosities, he’ll be saying the same thing, although by then he’ll have gone from being in a minority of theorists ( the situation today) to being in a very small minority of true-believers.

17. neo says:

–PW Possible, but that’s assuming continued null result, which is entirely plausible. If the LHC continues to provide null results even at 13-14TEV design energies and sufficient fb-1 & data analysis, what do you predict will happen to string theory research and interest? Do you think Witten, Susskind, Greene, Kaku, Hawking, et al will continue to work on it and promote it to a popular lay audience?

18. Peter Woit says:

neo,

Most of those you mention already have stopped working on string theory, and have likely already given up on the LHC vindicating string theory. On the other hand, people who have devoted 20-30 years to promoting something rarely publicly admit this was a mistake. I’d guess what will see will be a continuing refusal to publicly admit failure, coupled with half-hearted endorsements of string theory unification, while working on other things. Kind of like the situation now…