Rare decays of K mesons

Abstract

Kaon mesons offer a unique opportunity to search for physics beyond the Standard Model, by measurements of flavour physics observables in rare decays, search for decays violating lepton universality, flavour and number, and search for production of low mass feebly interacting particles. The experimental status of rare and forbidden kaon decays is reviewed; in particular the latest results on the $K_L\rightarrow\pi^0\nu\bar{\nu}$, $K^+\rightarrow\pi^+\nu\bar{\nu}$ and $K\rightarrow\mu^+\mu^-$ ultra-rare decays; the study of lepton universality with the $K^+\rightarrow\pi^+\mu^+\mu^-$ decay; the search for the lepton flavour and number violation decays $K\rightarrow\pi\mu e$; and the search for heavy neutral lepton production in $K^+\rightarrow l^+N$ ($l=e,\mu$) decays. Medium and long term prospects for experimental kaon physics are also discussed.