Monday, March 26, 2012

Still No Evidence Of SUSY At LHC

The latest round of LHC data further push up the mimimum masses of SUSY particles, if they exist at all.

If the squarks are outside of the LHC reach the lower limit on the gluino mass is now above 900 GeV, whereas if the squarks and gluino have comparable masses the limits on both are approaching the impressive value of 1.5 TeV.

The limitation on superpartner masses is model dependent, however:

[L]imits on the masses of the superpartners of the top quark still do not exist in a robust form. It is logically possible that the stop masses are relatively small, close to that of the top quark, while other colored superpartners are much heavier than TeV. This sort of spectrum is harder to achieve from the model-building perspective, but is favorable from the point of view of naturalness: light stops would cancel the dominant contribution to the Higgs mass from the induced in the Standard Model by the top quark. If that sort of spectrum is realized in nature then the limits discussed in the previous paragraphs do not apply, mostly due to the fact that the stop pair production cross section at the LHC is much smaller than that of gluinos and 1st generation squarks.

Of course, even if LHC doesn't find so much as a whiff of SUSY, one can still devise some sort of SUSY model with sufficiently heavy superpartners, or otherwise elusive phenomonology, to fit this data to some sort of model. Predictions made by SUSY theorists and string theorists, pre-LHC, aren't panning out. Even string theory backers are starting to sound disenheartened (I'm referring the the quoted material in the linked post, not the anti-SUSY blog author whose post is linked). So far, an experimental necessity for SUSY (or any beyond the Standard Model physics outside the neutrino sector) still isn't there and the entire theory is looking like one of the most expensive rabbit holes in the history of the human scientific endeavor.

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