20 March 2015: \(B^0\to K^*\mu^+\mu^-\): new analysis confirms old puzzle (LHCb CERN website)In July 2013, TRF readers were told about the 3.7 excess in these muon decays of B-mesons.
The complete 2011-2012 data, which was just 3 inverse femtobarns because we talk about LHCb (perhaps I should remind you that it is a "cheaper" LHC detector that focuses on bottom quarks and therefore on CP-violation and flavor violation), have been analyzed. The absolute strength of the signal has decreased but so did the noise so the significance level remained at 3.7 sigma!
The Quanta Magazine quickly wrote a story with an optimistic title
Why are we talking about these Antarctic birds here? It's because they are actually Feynman diagrams.
The Standard Model calculates the probability of the decay of the B-mesons to the muon pairs via a one-loop diagram – which is just the skeleton of the picture above – and this diagram has been called "penguin" by particle physicists who didn't see that it was really a female with big breasts and a very thin waistline.
But there may have been more legitimate reasons for the "penguin" terminology – for example, because it sounds more concise than a "Dolly Buster diagram", for example. ;-)
The point is that there are particular particles running in the internal lines of the diagram according to the Standard Model and an excess of these decays would probably be generated by a diagram of the same "penguin" topology but with new particle species used for the internal lines. Those hypothetical beasts are indicated by the question marks on the penguin picture.
Adam Falkowski at Resonaances adds some skeptical words about this deviation. He thinks that what the Standard Model predicts is highly uncertain so there is no good reason to conclude that it must be new physics even though he thinks that the it's become very unlikely that it's just noise.
Perhaps more interestingly, the Quanta Magazine got an answer from Nima who talked about his heart broken by the LHCb numerous times in the past.
Various papers have proposed partially satisfactory models attempting to explain the anomaly. For example, two months ago, I described a two-Higgs model with a gauged lepton-mu-minus-tau number which claims to explain this anomaly along with two others.
Gordon Kane discussed muon decays of B-mesons in his guest blog in late 2012, before similar anomalies became widely discussed by the experimenters, and he sketched his superstring explanation for these observations.
LHCb is a role model for an experiment that "may see an anomaly" but "doesn't really tell us who is the culprit" – the same unsatisfactory semi-answer that you may get from high-precision colliders etc. That's why the brute force and high energy – along with omnipotent detectors such as ATLAS and CMS – seem to be so clearly superior at the end. The LHCb is unlikely to make us certain that it is seeing something new – even if it surpasses 5 sigma – because even if it does see something, it doesn't tell us sufficiently many details for the "story about the new discovery" to make sense.
But it's plausible that these observations will be very useful when a picture of new physics starts to emerge thanks to the major experiments...
The acronym LHCb appears in 27 TRF blog posts.