Recent rumors supposedly coming from theorists at Harvard indicating that today would be the day that an announcement would be made of first evidence for a superpartner of a top quark have just been shot down. The talk at CERN on recent ATLAS searches for such a signal shows that nothing was found. An example of new limits is that if stops are produced via gluinos, the gluino has to have mass greater that 650 GeV and the stop a mass greater than 450 GeV.
Over the past year the LHC has conclusively falsified pre-LHC predictions that strongly interacting superpartners would easily be seen in the early data, with typical bounds on gluino masses now up to 1 TeV or so. One way to evade this conclusion has been to argue that the first two generations of squarks are quite heavy, with only the sbottoms and stops accessible to the LHC. A typical example of analysis of scenarios of this kind can be found here, where the conclusion is that naturalness requires that the mass of an stop be less than 400 GeV, and the mass of a gluino less than twice the mass of the stop. This is now starting to be in significant disagreement with the data.
The ATLAS analysis uses 2 fb-1 of data, with the promise of updated results using the full 4-5 fb-1 coming soon. The details of the new analyses were made public today here, here and here. For some background, see the latest posting at Resonaances. I hear that similar analyses now completed by CMS, with the full 2011 dataset, also show nothing. This week the earliest of the Winter conferences is going on, at Aspen, and tomorrow there will be talks updating the LHC SUSY situation from ATLAS, CMS, and theorist Matt Reece.
The LHC has done an impressive job of investigating and leaving in tatters the SUSY/extra-dimensional speculative universe that has dominated particle theory for much of the last thirty years, and this is likely to be one of its main legacies. These fields will undoubtedly continue to play a large role in particle theory, no matter how bad the experimental situation gets, as their advocates argue “Never, never, never give up!”, but fewer and fewer people will take them seriously. As always seemed likely, the big mystery the LHC will solve will be that of the Higgs: is it really there, and if so does it behave as the Standard Model predicts, or does it do something more interesting? Unfortunately we’re going to have to wait a while longer for more news on that front.
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