The other day I wrote a post reporting of the lowered expectations of SUSY enthusiasts, who now apparently look forward to seeing 2-sigma effects in the next Run data of the CMS and ATLAS collaborations. That would keep their hope going, apparently.

I would have no problem letting them wait for late 2015, when the first inverse femtobarns of 13 TeV collisions will have been given a look at. But another thing happened today which made me change my mind - a colleague noted in the comments thread of that article that the LHC experiments appear to not publish their 2- and 3-sigma excesses when they see them, waiting for more data that "wipes out" the fluctuation. This is a strong (and probably unsupported) claim!

So I decided to make the SUSY enthusiasts happy today, by posting here a hot-off-the-press 2.6-standard-deviations effect produced by a CMS search for an "edge" in dilepton events. What is an edge, you might well ask first of all. Reasonable question, so let me try and explain.

The production of supersymmetric particles in proton-proton collisions is expected to occur in pairs, and each of the two bodies is usually believed to produce a chain of decays whereby a standard model particle is emitted and the SUSY particle turns into a lighter one still belonging to the supersymmetric world, thereby conserving a quantity characterizing the supersymmetric particles. At the end of the chain, one usually finds a neutralino - a stable particle which escapes the detector unseen, leaving behind a signature of missing energy, an energy imbalance in the plane transverse to the beams direction, in addition to all the other produced particles.

Now, depending on the mass hierarchy of the SUSY particles, the chain of decays may result in the observation of charged leptons and missing energy; signatures involving electrons and muons are especially useful as they are rather free of nasty backgrounds from strongly-interacting particles. If one computes the invariant mass of pairs of leptons observed in an event, and the event is due to a chain decay of SUSY particles, the two leptons may exhibit a mass which distributes not as a Gaussian (as one would expect for a normal resonance), but rather a funny shape having a sharp edge at the maximum value.

The reason for the funny shape is that the two leptons do not come from the same particle decay; they come from the subsequent decay of two different SUSY particles. Hence their invariant mass can have any value, up to a maximum - they cannot exceed the mass difference between the two SUSY bodies. So for instance if particle X goes to an electron and thus turns into Y, and Y subsequently emits a muon and becomes Z, the mass difference X-Z is the maximum that the electron-muon pair can make.

A clean edge in the mass of lepton pairs would be a very striking signature of a SUSY particle decay chain. So CMS looked for a hint of such a structure in their data. The analysis is now public and you can see the money plot below. It is the invariant mass distribution of pairs of electrons or pairs of muons in events selected as potential signal candidates with some jet and missing energy requirements. The blue curve describes one background component, the red one is the Z->dilepton peak and continuum background, and the green curve is the signal shape, which has a typical triangular structure.

Striking, huh?

Aha! No, unfortunately I am kidding - the plot above is a Monte Carlo simulation of what the data would look like if there was a SUSY signal there! Otherwise, I would not be using mild tones in this post; I would be screaming that we have finally made the discovery of the century! No. The real CMS data is shown below.

As you can see, on top of the expected background distribution one could see a smallish triangular-shaped excess at low invariant masses. Its significance can be estimated as a 2.6 sigma effect. Of course, as I explained in the previous post (and I am not doing it again here), there is no room for excitement; but it is still encouraging for those of you who strongly believe that some SUSY signal will eventually be found at the LHC. Who knows - this might grow to 5 sigma next year...

If you need more information about the analysis, you can find it in the slides shown yesterday by Kostas Theofilatos from ETH Zurich, or at this link. Enjoy it, Sven! (to others: Sven is the commenter of the previous post who lamented that we do not publish 2- and 3-sigma effects often enough).

A SUSY Edge Signal ? CMS Sees A 2.6 Sigma Excess !

## Comments

Tommaso Dorigo | 08/03/14 | 02:10 AM

Dilepton+MET from h->WW* is not that small as pointed out in one of your previous blogs.

PJ (not verified) | 08/03/14 | 03:50 AM

Tommaso Dorigo | 08/03/14 | 05:37 AM

There seems to be an idea around that all theorists love Susy and would be delighted to see her put in an appearance. I guess that this is an understandable error if you read moronic blogs like that of Lubos Motl, but I assure you that this opinion is far from universal among us. In fact many of us regard super symmetry as a childish and very ugly idea, the kind of thing that a desperate theory PhD might invent during the final year of his candidature. Please bear this in mind: we aren't all as laughably lacking in taste as LM.

Elbi Gilgen (not verified) | 08/03/14 | 05:12 AM

Lubos is an advocate of M-theory. M-theory is far from being a childish area of study.

kneemo (not verified) | 08/03/14 | 09:24 AM

Hank Campbell | 08/03/14 | 10:04 AM

Hank, I work on M-theory as mathematics and physics. It is an ongoing project but the structure is so rich and deep, it also gives hints at unifying mathematics itself. For example, I can study the Leech lattice, and be happy connecting it to the structures of sporadic finite groups and automorphic forms. On the other hand, via M-theory, in the nonperturbative regime, the Leech lattice is a charge space of a Planck scale black hole. The gauge group of transformations of this black hole is a discretized exceptional group! These kinds of insights happen all the time as we further explore M-theory.

As for predictions, there should exist tachyons and graviphotons that are measurable. One approach is via condensed matter experiments where one can effectively create magnetic monopoles in the bulk of topological insulators. Another approach reveals a graviphoton contribution to the mass of cooper pairs in superconductors. If you look at Kitaev's classification of superconductors & topological insulators you'll notice they are described by the same symmetric spaces as those found in supergravity. The higher dimensional condensed matter systems actually correspond to those of N=8 supergravity. This is why many string theorists are now collaborating with condensed matter physicists, studying effective axions and dyons that emerge within these exotic materials. This sounds like standard science to me.

As for predictions, there should exist tachyons and graviphotons that are measurable. One approach is via condensed matter experiments where one can effectively create magnetic monopoles in the bulk of topological insulators. Another approach reveals a graviphoton contribution to the mass of cooper pairs in superconductors. If you look at Kitaev's classification of superconductors & topological insulators you'll notice they are described by the same symmetric spaces as those found in supergravity. The higher dimensional condensed matter systems actually correspond to those of N=8 supergravity. This is why many string theorists are now collaborating with condensed matter physicists, studying effective axions and dyons that emerge within these exotic materials. This sounds like standard science to me.

kneemo (not verified) | 08/03/14 | 10:43 AM

So it isn't Lubos you are defending, it is you. That's fine, I am not disparaging your work, I hope it comes to fruition, just like I hope the Standard Model does. I just want to able to explain the world according to natural laws and the flavor is unimportant to me.

But invoking maths isn't helping justify M-Theory as an actual theory. As you know better than anyone, every month on arXiv time travel can be mathematically possible, that does not make it a theory of time travel. All it does is undermine public acceptance of science about what is real and what is still conjecture.

But invoking maths isn't helping justify M-Theory as an actual theory. As you know better than anyone, every month on arXiv time travel can be mathematically possible, that does not make it a theory of time travel. All it does is undermine public acceptance of science about what is real and what is still conjecture.

Hank Campbell | 08/03/14 | 10:56 AM

Hank

You did not address the condensed matter applications of M-theory and supergravity. Please offer an opinion, as topological insulators, which are real-life materials like bismuth teleride, are at the heart of a whole new technological breakthrough, called dyonics.

You did not address the condensed matter applications of M-theory and supergravity. Please offer an opinion, as topological insulators, which are real-life materials like bismuth teleride, are at the heart of a whole new technological breakthrough, called dyonics.

kneemo (not verified) | 08/03/14 | 11:03 AM

I am not going to argue with you about physics hypotheses - I certainly hope you are better at it than me, since my education in condensed matter physics happened almost 30 years ago and, as you know, almost all of it that was taught to me then is mostly wrong today. However, if you can show evidence that bismuth telluride came about because of M-Theory, though that compound originated in the 1950s, we'd all be intrigued to see it.

All I said was M-Theory is not a theory. By the definition of theory, it is not. It's a proper name, just like String Theory.

All I said was M-Theory is not a theory. By the definition of theory, it is not. It's a proper name, just like String Theory.

Hank Campbell | 08/03/14 | 11:44 AM

Yes, many of the materials have been in use since the 50's, but not used to produce magnetic monopoles. Supergravity has been shown to arise from M-theory toroidal compactifications, and supergravity is the proper theoretical framework to study many of the exotic phenomena arising in superconductors and topological insulators. Hence, as an explanatory framework to describe such observed phenomena (as well as make predictions for the yet to be discovered higher dimensional topological insulators and superconductors), M-theory is indeed a true scientific theory.

kneemo (not verified) | 08/03/14 | 17:09 PM

Tommaso Dorigo | 08/04/14 | 03:38 AM

Condensed matter applications of M-theory are irrelevant in deciding whether or not M-theory is a correct extension of the standard model. When one says M-theory has applications in condensed matter physics, what one means is that the mathematical tools and insights developed by those studying M-theory have resulted in advances in condensed matter physics. But the fact that insights gleaned from M-theory have proven useful in condensed matter does not speak to whether or not an M-theory extension to the standard model is correct. It also does not count as a "prediction" of M-theory in the realm of particle physics. If you want to argue that M-theory has helped advance condensed matter physics, do it on a condensed matter physics blog. Pretending that fact has something to do with particle physics is misleading.

KJ (not verified) | 08/04/14 | 16:10 PM

M-theory is not an extension of the standard model. It is a completion of string theory and supergravity.

kneemo (not verified) | 08/04/14 | 16:22 PM

Tommaso Dorigo | 08/05/14 | 00:57 AM

Zephir (not verified) | 08/04/14 | 07:21 AM

BTW The finding of century in physics are the cold fusion and scalar wave beams - not the stuffs which have only meaning for few theorists involved. The physicists are here for to serve the civilization, not vice-versa.

Zephir (not verified) | 08/04/14 | 07:23 AM

I am a SUSY sustainer but the signal seems to week.

Thx for keeping alive this blog.

Thx for keeping alive this blog.

Bogdan (not verified) | 08/11/14 | 09:46 AM

yes, this edge caused some excitement at SUSY14. ;-)

Your SUSY comparison above assumes a certain cross section value, where a lower one (which is certainly possible...) could correspond exactly to the CMS data.

Two questions:

Do the 2.6 sigma include the LLE effect?

What does the ATLAS data say?

Cheers, Sven