The Path Towards the First New Physics Discovery using Flavour Physics
In 2013 LHCb announced the observation of a large tension between the measurement of an observable called P5' and our SM prediction. This observable that is part of the angular distribution of the decay Bd->K*(->Kpi)l+l- was constructed to maximize the sensitivity to New Physics and suppress the form factor dependence at leading order. This evidence of New Physics (above 3.7 sigmas) was the first and the largest of the so-called B-Flavour anomalies.
The following years not only brought a confirmation of this evidence from LHCb with more data (Moriond EW 2015), but other experiments (Belle and ATLAS) also confirmed the presence of the anomaly, Besides other decay channels exhibited deviations coherent with P5'. In parallel observables testing the universality of the coupling of gauge bosons to all lepton families coming from ratios of branching ratios of semileptonic decays to muons versus electrons also shown deviations with respect to the SM prediction. Our latest global analysis of 180 observables coming from decays governed by b->sll and b->s gamma found significances of different New Physics hypothesis (or patterns of New Physics) up to 5.9 sigmas. This is a measure of the coherence of deviations and tell us quantitatively by how much the SM hypothesis is disfavoured with respect to the different New Physics hypothesis or patterns.
Now we are entering the next step, to discern what type of New Physics we have found. Here the prejudices in favour or against certain models can be dangerous, and more than ever it is necessary to keep an open minded approach and try to think always out of the box removing old hypotheses.
We are not to tell nature what she’s gotta be. … She's always got better imagination than we have. [Richard Feynman]
The following five years will be exciting, news from LHCb and Belle-II can provide us with key information to disentangle the right pattern of New Physics and this in turn can guide us in the construction of the correct fundamental model that will supersede the SM of particle physics.