You may have seen by now claims from various sources about evidence for SUSY coming from CMS, for instance Hints of New Physics Crop Up at LHC, A Lifeline for Supersymmetry?, and CMS sees SUSY-like trilepton excesses. This nonsense is all due to Matt Strassler, who for some reason thought it was a good idea to post a blog entry Something Curious at the Large Hadron Collider that starts off:
Finally, something at the Large Hadron Collider (LHC) that does not seem to agree that well with the predictions of the equations of the Standard Model of particle physics.
followed by various caveats, which include though the advice:
But this is clearly something to watch closely over the coming months.
As one could easily have predicted, this got picked up by the media and various blogs, mostly dropping the caveats. In a later more detailed posting, Matt carefully three times in italicized red explains that “The excess will probably disappear”. He does continue to claim that “particle physicists are paying close attention” to this statistically insignificant discrepancy between data and theory, something I suspect was true before his blog posting for an equally statistically insignificant number of particle physicists.
During this past week or so, there has been a lot of various news about SUSY at the LHC, all of it bad. For some background, one should look at Mike Peskin’s write-up of his summary talk at LP2011, which he posted last week to the arXiv. See pages 37-41 for his discussion of the state of SUSY. He explains why one would expect that all SUSY mass terms are of the order of a few hundred GeV, with the Tevatron bounds on gluino and squark masses (around 300 GeV) already making one suspicious. Similar LHC bounds are already around 1000 GeV, getting close to the limit (around 1200 GeV) of what can be produced at current beam energy. When the LHC comes back on-line with higher beam energy in 2014, these bounds should then go up to 2000 GeV or more. Much has been and is being made of the fact that one can find SUSY models that evade these bounds, with LHC results then giving lower limits in the range 500 GeV and above.
As the LHC experiments become sensitive to hypothetical new particles with TeV masses, we are reminded of the phrase from the Latin Requiem Mass:
Confutatis maledictis, flammis acribus addictis, voca me cum benedictus.
A loose translation is: Thousands of theory papers are being tossed into the furnace. Please, Lord, not mine!
Before the startup of the LHC, I expected early discovery of events with the jets + missing transverse energy siignature of supersymetry. It did not happen. A particularly striking comparison is shown in Fig. 33. On the left I show the expectation given in 2008 by De Roeck, Ellis, and their collaborators for the preferred region of the parameter space of the constrained Minimal Supersymmetric Standard Model (the cMSSM, also know as MSUGRA). The red region is the 95% confidence expectation. On the right, I show the 95% confidence excluded region from one of the many supersymmetry search analyses presented by CMS at LP11. No reasonable person could view these figures together without concluding that we need to change our perspective.
Peskin goes on to argue though that the thing to do is not to abandon SUSY since it hasn’t shown up where it was supposed to, but to “acknowledge that, to test SUSY, we must search over the full parameter space of the the model”. The obvious problem with this is that the “full parameter space of the model” is huge, containing all sorts of corners that will never be accessible to the LHC, or that can be made arbitrarily difficult to rule out, requiring intensive effort from LHC experimenters for decades to come.
For details on what has been going on, various recent sources to consult include Anyes Taffard’s FNAL talk on ATLAS SUSY searches (“SUSY was NOT ‘just around the corner’ … must be hiding well … Or may be … need to go back to the drawing board”) and the many talks at the Berkeley Workshop on Searches for Supersymmetry at the LHC which included a huge array of negative SUSY results, including the one that for some reason got Matt so excited. Besides the kinds of models that Peskin expected to see at the LHC, lots of other more obscure ones are being ruled out by new LHC analyses. These include some that had gotten a lot of popular attention, such as split supersymmetry and F-theory models. These predicted things like long-lived gluinos or staus, which have now been searched for and ruled out in regions where they were supposed to show up. For example see here for more about F-theory and the stable staus, which CMS now says are not there where they were supposed to be (below 300 GeV).
For some other recent news, see the talks at the BNL conference running the past couple days, A First Glimpse of the Tera Scale.
Finally, for the best in recent HEP news, see this from Warren Siegel.
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