Tommaso Dorigo has discussed something that may be interesting – a hint of new physics coming from the LHCb experiment:
A Four-Sigma Evidence Of New Physics In Rare B Decays Found By LHCb, And Its InterpretationThe deviation will be described in the LHCb-PAPER-2013-037 paper, now in preparation. Locally, it is a \(3.7\)-\(4.0\sigma\) effect which is reduced to \(2.5\)-\(2.8\sigma\) once you take the 24 bins into account (look-elsewhere effect). See page 13 of Nicola Serra's presentation in Stockholm.
We just described how strong the evidence is. But what events is the evidence about? Well, it is about the decay of the neutral \(B\)-mesons\[
B^0 \to K^* \mu^+ \mu^-, \quad K^*\to K^+ + \pi^-.
\] Recall that the asterisk denotes a virtual particle in this experimental jargon. When some "new observables" are used, they see the aforementioned excess of events approximately in bins with the transferred momentum\[
1\GeV\lt \sqrt{|q^2|}\lt 3\GeV
\] or so, especially between \(2\GeV\) and \(3\GeV\).
Dorigo recommends you a three-day-old hep-ph paper by Sebastien Descotes-Genon, Joaquim Matias, and Javier Virto
Understanding the \(B\to K^* \mu^+\mu^-\) AnomalyThis paper is aware of the anomaly we have mentioned and proposes a parameterization of the anomaly – some new physics' contribution to the "Wilson" coefficient \({\mathcal C}_9\) of the semileptonic operator\[
{\mathcal O}_9 = \frac{e^2}{16\pi^2} (\bar s\gamma_\mu P_L b) (\bar \ell \gamma^\mu\ell).
\] The operators with subscripts \(7\) and \(10\) are discussed, too. Who is contributing to the coefficient isn't really clarified so this whole discussion remains somewhat boring and technocratic.
However, some TRF readers with a very good memory should have a deja vu feeling. Haven't we seen something similar?
Yes, we have. First of all, in May 2012, BaBar reported a \(3.4\sigma\) excess in \(\tau\nu\) decays of the B-mesons. But the \(\tau\) leptons were involved so it's a different final state than the final states considered here.
In March 2013, I described some potentially huge, \(7\sigma\) or \(9\sigma\) excesses in pion and kaon decays of the charged \(B\)-mesons seen by the LHCb. Note that journalists often present each experiment that agrees with the Standard Model as strong if not lethal evidence against new physics but they get it upside down: it's enough to find one experiment that disagrees with the Standard Model to falsify that good old theory and it's plausible that we already know such experiments.
Most similarly, in November 2013, Gordon Kane wrote a TRF guest blog about the superstringy predictions for the\[
B^0_s\to \mu^+\mu^-
\] decays which are similar to the decays discussed in this text but they didn't including the virtual kaon. The stringy prediction looked very accurate to them (LHCb and CMS just published their combined data on this very process that are compatible with the Standard Model) and the processes mostly depended on the moduli – the scalar fields encoding the oscillating shape of the compactified dimensions whose particles should be at least as heavy as \(30\TeV\) or so for cosmological or astrophysical reasons.
So some evidence of new physics may already be "out there" but time and independent observations will probably be needed before we will feel any certain about these claims – and, equally if not more importantly, about the type of new physics that causes these anomalies.
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