Meson-antimeson mixing
arXiv:2510.11716
Abstract
Meson-antimeson transitions are flavor-changing neutral current processes in which the strangeness, charm, or beauty quantum number changes by two units. In the Standard Model (SM) these transitions originate from box diagrams with two W bosons. They permit the preparation of time-dependent, oscillating quantum states which are superpositions of a meson and its antimeson. By studying their decays one gains information on both the meson-antimeson mixing amplitude and the decay amplitude involved and one can measure complex phases quantifying the violation of charge-parity (CP) violation. I present a comprehensive overview on the topic, starting with phenomenological presentations of -, -, -, and - mixing. Highlights are the discovery of the violation of CP and other discrete symmetries, the predictions of the charm quark and its mass and a heavy top quark, and the confirmation of the Kobayashi-Maskawa mechanism of CP violation. Further sections cover the theoretical formalism needed to describe meson-antimeson mixing and to calculate observables in terms of the fundamental parameters of the SM. I discuss the unitarity triangle of the Cabibbo-Kobayashi-Maskawa matrix, which is used to visualize how various CP-violating and CP-conserving quantities combine to probe the SM. I describe the emergence of precision flavor physics and the role of reliable theory calculations to link - mixing to - mixing, which was essential to confirm the Kobayashi-Maskawa mechanism, and present the current status of theory predictions. Today, the focus of the field is on physics beyond the SM, because meson-antimeson mixing amplitudes are sensitive to virtual effects of heavy particles with masses which are several orders of magnitude above the reach of current particle colliders.
Review article prepared for "Encyclopedia of Particle Physics", 50 pages, 9 figures, v2: typos corrected, references added, sentence clarified