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 RK of the K±→e±ν and K±→μ±ν decay rates has been performed using the full data set collected by the NA62 experiment in 2007–2008. The result is RK=(2.488±0.010)×10−5, in agreement with the Standard Model expectation. An improved upper limit on the rate of the lepton number violating K±→π∓μ±μ± 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 at 10% precision is discussed.