What surprised me most about today’s Run 2 results (see here) was that CMS and ATLAS were able to already significantly push up limits on superpartner masses, especially the gluino mass. Limits on the gluino mass went from 1.3-1.4 TeV in Run 1 to something like 1.6-1.8 TeV in the new Run 2 data (this depends on exactly what channels one is looking at). This not only kills off Gordon Kane’s string theory prediction of a 1.5 TeV gluino, but it also removes a large chunk of the remaining possible mass region that the LHC will be able to access. And it wasn’t just the gluino: ATLAS quoted limits on sbottom masses moving up from 650 GeV in Run 1 to 850 GeV today. Whatever you thought the remaining probability was for SUSY after the negative Run 1 results, it’s significantly smaller today.
Almost all the news has been about the possible diphoton excess, ignoring the quite significant story about SUSY. Davide Castelvecchi at Nature though today talked to Michael Peskin, who has been one of the more consistent proponents of SUSY over the years, and this was part of his story:
Meanwhile, searches for particles predicted by supersymmetry, physicists’ favourite extension of the standard model, continue to come up empty-handed. To theoretical physicist Michael Peskin of the SLAC National Accelerator Laboratory in Menlo Park, California, the most relevant part of the talks concerned the failure to find a supersymmetric particle called the gluino in the range of possible masses up to 1,600 GeV (much farther than the 1,300-GeV limit of Run 1). This pushes supersymmetry closer to the point where many physicists might give up on it, Peskin says.
I had thought that the “physicists give up on SUSY” story wouldn’t get going until next year, but maybe it’s already started.
Update: In just a few hours after the announcement already 10 papers on hep-ph devoted to explaining the diphoton resonance. SUSY explanations not among the popular ones.
Update: Another eight or so papers explaining the diphotons. And the press has the obvious explanation: string theory:
The idea seems to be that since people were looking for Randall-Sundrum gravitons (which somehow counts as string theory) then if they find something in the diphoton spectrum it could be a graviton. I’m no expert, but none of the dozens of hep-th papers seem to discuss this possibility, and the papers about searches for Randall-Sundrum gravitons (like this one) set limits way above a TeV. On the other hand, I don’t doubt that some “string vacuum” can be found that will explain the diphotons, and that we’ll hear more about it in the press.