HCP2012 Higgs results will be announced Wednesday (I’m hearing that CMS tau-tau signal is .7 +/- .5 x the SM value), but interest may focus much more on the strong SUSY exclusions being announced there. So far the LHCb result on B(s)->mu+mu- has been the one getting all the attention, with a BBC News story describing it as “a significant blow to the theory of physics known as supersymmetry”. In the story experimentalist Chris Parkes describes the current situation as “Supersymmetry may not be dead but these latest results have certainly put it into hospital.” John Ellis is having none of this though:
Supporters of supersymmetry, however, such as Prof John Ellis of King’s College London said that the observation is “quite consistent with supersymmetry”.
“In fact,” he said “(it) was actually expected in (some) supersymmetric models. I certainly won’t lose any sleep over the result.”
The bad news for SUSY out of Kyoto however does not end there. ATLAS and CMS are both coming out with new analyses using this year’s 8 TeV data which significantly expand previous limits on SUSY, getting close to ruling out popular last-ditch efforts to save the theory. For the latest, look at this HCP2012 page, this ongoing Chicago workshop, and CMS results announced here (like this), ATLAS results announced here.
The last ditch effort to save the idea that SUSY solves the so-called hierarchy problem goes under the name of “Natural Supersymmetry”. It involves moving most superpartners to high masses where the LHC can’t see them, keeping only the stop, sbottom, gluinos, and a couple neutralinos at LHC accessible masses. If you look at the bounds given on these masses for instance here, and compare to the latest LHC results, you’ll see that there’s trouble on all fronts for this idea, which is now very close to being essentially ruled out.
Gordon Kane is fighting back against the BBC by going to Lubos Motl’s blog to argue that the LHCb result is no problem for his string theory “predictions”. You see, his “prediction” is now that most superpartners are way beyond what the LHC can see, so not only is the LHCb result not negative for SUSY, but it “adds to the evidence for supersymmetry and for M/string theories”. Kane doesn’t mention any of the other SUSY excluding results coming out this week, or their implications for his “prediction” of the gluino mass. Last year Kane was telling Tommaso Dorigo
I and others expect this decay to tops and bottoms is the signature by which gluinos will be found, with masses well below a TeV
and his slides had a gluino mass prediction of about 600 GeV. Late last year he was arguing that the gluinos would be seen by this past summer. More recently, he’s modified the graph in his slides to move the gluino up to 1 TeV. This week ATLAS reports a new gluino mass limit of 1.24 TeV, so Kane will have to modify his slides yet again.
The combined effect of the bad press and the devastating experimental results on the 30 year old SUSY juggernaut will be interesting to follow. At this point, it is hard to see how one could rationally expect anything positive for SUSY to come out of further analyses of the 7 TeV and 8 TeV data. I suppose many will try and delay acknowledging failure by saying one must wait for the 13 TeV data, which we won’t see until 2015 or so, but I don’t think this is going to convince many people.
Update: Matt Strassler objects to the BBC article, on the grounds that one should not describe what is happening to SUSY in terms of “blows” or it getting hurt. Instead, one should stick to saying it is getting “cornered”, and he agrees that “the cornering of supersymmetry is well underway”. The question this raises though is what happens to SUSY once it is cornered if you object to it getting hurt. I suspect the hope of many SUSY theorists is that even once cornered, SUSY will continue to be well-treated, receiving annual $3 million prizes and being taught to new generations of graduate students.
Update: The Daily Mail covers this, with the non-tabloid-like headline Experts take conflicting opinions as to how far results support the theory of super symmetry. Oliver Buchmueller joins Gordon Kane in the bizarre game of claiming negative results as positive for SUSY, making the argument
‘This is another piece in the puzzle and with it the world appears even more SM-like,’ he said. ‘It supports SUSY, because that is the only theory that can include the Standard Model in a wider concept of New Physics.’
Update: More about this from Matt Strassler, who writes about Theory Killers at the HCP conference. I guess it’s still all right to kill “theories”, as long as SUSY herself doesn’t get hurt.
Update: The rather odd controversy over the BBC story goes on, with Lubos Motl and Matt Strassler continuing to argue that the scientific method implies that SUSY can’t get hurt. I would have thought that it was uncontroversial that if proponents of an idea claimed that it would be vindicated by an experiment, and the experimental result came back negative, that was not good for the idea, but, at least for SUSY, that doesn’t seem to be the case. Yes, SUSY comes in infinite varieties, many of them never testable, but the experimental results shooting down its versions sold as the most well-motivated ones do have implications for its health. I see no reason why one needs to wait for the LHC to examine every possible remote corner of parameter space that it can access before remarking on what has happened.
Update: It is being pointed out that the BBC story is inaccurate: the LHCb bounds on Bs meson decays that rule out a large chunk of SUSY theory space were already there in March. So, on this front SUSY entered the hospital in March, not this past week. Of course, an even bigger inaccuracy in the BBC story was describing SUSY as an idea that has only encountered serious health problems recently, rather than many years ago…
Update: There’s now a fourth rant from Matt Strassler about the LHCb result, a topic on which he has become a bit of a zealot. The point being made is that SUSY was already so badly injured pre-LHCb that they didn’t make things any worse. It’s quite possible he’s right about this, would be interesting to hear a response from the LHCb people.
Update: A characteristically lucid posting on the topic from Jester: BS and SUSY.
To conclude, you should interpret the LHCb measurement of the Bs→μμ branching fraction as a general, strong bound on theories on new physics coupled to leptons and, in a flavor violating way, to quarks. In the context of SUSY, however, there are far better reasons to believe her dead (flavor, CP, hierarchy problem, direct searches). So one should not view Bs→μμ as the SUSY killer, but as just another handful of earth upon the coffin