## Tuesday, April 18, 2017

### LHCb insists on tension with lepton universality in $$1$$-$$6\GeV^2$$

The number of references to B-mesons on this blog significantly exceeds my degree of excitement about these bound states of quarks and antiquarks but what can I do? They are among the leaders of the revolt against the Standard Model.

Various physicists have mentioned a new announcement by the LHCb collaboration which is smaller than ATLAS and CMS but at least equally assertive.

Another physicist has embedded the key graph where you should notice that the black crosses sit well below the dotted line where they're predicted to sit

and we were told about the LHCb PowerPoint presentation where this graph was taken from.

To make the story short, some ratio describing the decays of B-mesons that should be one according to the Standard Model if the electron, muon, and tau are equally behaved – except for their differing masses which are rather irrelevant here – ends up being $\Large {\mathcal R}_{K^{*0}} = 0.69 + 0.12 - 0.08$ especially in the interval of momentum transfer $$q^2 \in (1,6)\GeV^2$$.

There are some similar deviations at higher values of $$q^2$$, it's always about 2.2-2.5 standard deviations below the Standard Model. Sadly, it seems that neither BaBar nor Belle saw these deficits: their mean values are slightly greater than one although their error margin was greater than that of the LHCb collaboration. On the other hand, the deficit seems rather compatible with the LHCb's recent announcements based on a (hopefully) disjoint set of decays.

An obvious reaction is that the deviation in this low-energy range isn't too exciting, anyway, because

Well, unless it's some new physics (new even for Jester) that affects this energy range. ;-)

I find this deviation rather small and our survival of the 4-sigma excess at $$750\GeV$$ should have made us a little bit more demanding when it comes to the significance level that is needed to make us aroused. But those who are interested in the existing or potentially emerging experimental anomalies should be aware of this deviation because the competition in this field is very limited.