According to the BBC, it was a heavy blow. According to a member of the LHCb experiment quoted in the article, it put the theory “in the hospital.” The reality? Nobody even suffered a scratch.
On Monday I wrote about a new measurement by the LHCb experiment at the Large Hadron Collider [LHC] of a rare process, reported at the HCP 2012 conference in Kyoto (a link to the talks can be found at this link), in which a B_s meson decays to a muon and an anti-muon (click here for more details of the physics process.) It’s a very important measurement, definitely! But whilelistening to theorist Gino Isidori’s talk in which he briefly discussed this measurement, I was a little puzzled about an inconsistency between what LHCb had done and said in the past, and what they had done and were saying now, in particular as was reported/implied by the BBC.
When I chatted with him later, Isidori reminded me exactly what LHCb reported in March, and how it compares to what they report now.
- March: LHCb reported that at most 4.5 per billion B_s mesons decay this way (at 95% confidence)
- November: LHCb reports about 3.5 per billion B_s mesons decay this way, and at 95% confidence the rate is at least 1.1 per billion and at most 6.4 per billion.
Notice that the new measurement raises the upper limit on how often this process occurs. This upward shift is not an indication of a problem; it’s probably just an ordinary statistical effect that arises from having small amounts of data. But it makes the constraints from this measurement — on the many variants of supersymmetry, and on other theories — a little weaker, if anything. Most of the supersymmetric (and other) models that would be constrained by this measurement lead to a higher rate than in the Standard Model (where it is predicted to be about 3.2 ± 0.3 per billion). So a higher upper limit means fewer of these variants are excluded by the data. All in all, the constraints on supersymmetric (and other) models are little changed, and perhaps somewhat weaker than they were in March. Isidori and his colleagues have worked this out, and I’ll try to get details from them next week.
No need to take my word for it, or even Isidori’s. Professor Michelangelo Mangano of CERN, apparently having spoken independently to other experts, made exactly the same point on page 41 of his summary talk concluding the conference. (By the way, it was a great talk, and I recommend that experts read it.)
Well! So much for the big BBC headline! [Most likely the public will never learn about this; a news report describing more accurately what this really means for supersymmetry etc. probably will not appear at all on the BBC, and even if it does, it certainly won't get a big attention-grabbing headline. It's sad that this inherent bias in media reporting ensures the public gets an unhealthy dose of incorrect scientific information and rarely gets the antidote.]
None of this at all diminishes LHCb’s accomplishment! They’ve made a great measurement, for which they deserve big congratulations. A round of applause, please!! But let’s not overstate its immediate impact. As the measurement becomes more precise, its impact will gradually become greater, and even more so when it is combined with similar measurements from ATLAS and CMS.
But meanwhile, there were powerful and truly new constraints on supersymmetry (and other theories) reported at this conference, and they came from ATLAS and CMS, in their searches for effects from superpartner (and other) particles. I told you about a small number of these searches a couple of days ago (by the way, I learned meanwhile that CMS has a search that is similar to the one I mentioned from ATLAS involving bottom quarks) and maybe I’ll point out a few others next week, if I have the energy.