Flavour Expedition to the Zeptouniverse

Abstract

After the completion of the Standard Model (SM) through the Higgs discovery particle physicists are waiting for the discovery of new particles either directly with the help of the Large Hadron Collider (LHC) or indirectly through quantum fluctuations causing certain rare processes to occur at different rates than predicted by the SM. While the later route is very challenging, requiring very precise theory and experiment, it allows a much higher resolution of short distance scales than it is possible with the help of the LHC. In fact in the coming flavour precision era, in which the accuracy of the measurements of rare processes and of the relevant lattice QCD calculations will be significantly increased, there is a good chance that we may get an insight into the scales as short as 10^{-21} m (Zeptouniverse) corresponding to energy scale of 200 TeV or even shorter distance scales. We discuss the requirements that have to be met for such a flavour expedition to the Zeptouniverse to be successful. In particular we emphasize the power of correlations between flavour observables in the search for New Physics and identify a number of correlations that could allow to discover NP even if it would appear at the level of 20% of the SM contributions. The correlation between K^+\to\pi^+\nu\bar\nu, B_s\to\mu^+\mu^- and \gamma extracted from tree-level decays within the SM is one of them. We address the recent data on B_{s,d}\to\mu^+\mu^- and the anomalies in B_d\to K(K^*)\mu^+\mu^-, including breakdown of lepton flavour universality. We emphasize the correlations of B_d\to K(K^*)\mu^+\mu^- with B_d\to K(K^*)\nu\bar\nu. We summarize the recent study of K\to\pi\nu\bar\nu and B_{d,s}\to\mu^+\mu^- decays which demonstrates that these decays play important roles in finding out what happens in the Zeptouniverse.