CP Violation in the SM, Quantum Subtleties and the Insights of Yogi Berra

Abstract

Our knowledge of flavour dynamics has undergone a `quantum jump' since just before the turn of the millenium: direct CP violation has been firmly established in $K_L \to \pi \pi$ decays in 1999; the first CP asymmetry outside $K_L$ decays has been discovered in 2001 in $B_d \to \psi K_S$, followed by $B_d \to \pi^+\pi^-$, $\eta^{\prime}K_S$ and $B \to K^{\pm}\pi^{\mp}$ establishing direct CP violation also in the beauty sector. Counterintuitive, yet central features of quantum mechanics like meson-antimeson oscillations and EPR correlations have been crucial in making such effects observable. The CKM dynamics of the Standard Model (SM) of HEP allow a description of CP insensitive and sensitive $B$, $K$ and $D$ transitions that is impressively consistent even on the quantitative level. We know now that at least the lion's share of the observed CP violation is provided by the SM. Yet these novel successes do not invalidate the theoretical arguments for it being incomplete. We have also more direct evidence for New Physics, namely neutrino oscillations, the observed baryon number of the Universe, dark matter and dark energy. While the New Physics anticipated at the TeV scale is not likely to shed any light on the SM's mysteries of flavour, detailed and comprehensive studies of heavy flavour transitions will be essential in diagnosing salient features of that New Physics. Strategic principles for such studies are outlined.