Kaon Experiments

Abstract After $CP$ violation was discovered in the $K_L \rightarrow \pi ^+ \pi ^-$ decay, many theories were proposed to explain it, and the Kobayashi–Maskawa model and the Superweak model lasted for many years as strong candidates. High-precision kaon experiments with many new techniques and improvements rejected the Superweak model and supported the Kobayashi–Maskawa model in the 1990s. Since then, rare kaon decay experiments have studied $K \rightarrow \pi \nu \overline{\nu }$ decays to search for $CP$ violation caused by new physics beyond the Standard Model. Various techniques have been developed to increase the sensitivity and to suppress backgrounds.