Flavour Physics

The particles of the Standard Model are organized in three families, which, apart from large differences in the mass, are perfect copies of each other. Heavy flavor physics deals with the properties of the heaviest quarks that is the quarks of the third family (top and bottom) and to a lesser extent those of the second family (charm and strange). Long range goals are to understand why there are three families and why there is such an extreme mass pattern (the top quark is more than hundred times heavier than its counterpart in the second family, the charm quark).

Another crucial aspect of heavy flavor physics is the study of CP violation (CP is the combined operation of interchanging particles with antiparticles, C, and looking at the world in a mirror, i.e. parity P). CP violation is one of the ingredients necessary to explain the huge abundance of matter over antimatter that is observed in the universe. The Standard model does predict CP violation, but only in processes where all three families take part and therefore involves processes with the bottom or top quark. These processes to be investigated at current and future experiments also provide us with a promising window for physics beyond the Standard Model.

The present status of flavour physics is characterized by a large number of precision results on B, D and K decays which, within the available experimental and theoretical accuracy, broadly confirm the Standard Model (SM) picture of flavour and CP violation. Flavour physics is dominated by non-perturbative strong interaction effects but very occasionally there are tantalizing hints of new physics, such as the recently measured discrepancy between the time-dependent CP asymmetry in b→ ccs and b→ qqs (penguin) transitions.

An important stratagem in using flavour physics to explore the limits of the SM has been the study of the rare processes which in the SM are dominated by loop effects and which therefore are expected to have significant contributions from the heavy particles present in theories of new physics. At present we do not know the mass scales of the new physics and this ignorance hinders the development of an optimal strategy for flavour physics. This will change radically once new physics has been discovered at the LHC.

In the future, the key role of flavour physics will be to differentiate between various new physics models by measuring or constraining couplings, which will be difficult or impossible to do from direct searches. Flavour physics is therefore an essential complement to the direct production of new particles at the LHC.