Kaon experiments at CERN: NA48 and NA62

Searches for violation of lepton flavour universality and lepton number conservation in kaon decays by the NA62 and NA48/2 experiments at CERN, status and future plans of the CERN kaon programme are presented. A precision measurement of the helicity-suppressed ratio $R_K$ of the $K^\pm\to e^\pmν$ and $K^\pm\toμ^\pmν$ decay rates has been performed using the full data set collected by the NA62 experiment in 2007--2008. The result is $R_K=(2.488\pm0.010)\times10^{-5}$, in agreement with the Standard Model expectation. An improved upper limit on the rate of the lepton number violating $K^\pm\toπ^\mpμ^\pmμ^\pm$ decay from the NA48/2 experiment (2003--2004 data set) is presented. Finally, the NA62 project aiming at a measurement of the branching ratio of the ultra-rare decay $K^+\toπ^+ν\barν$ at 10% precision is discussed.

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