RECENT RESULTS ON RARE KAON DECAYS FROM NA48/2 AND NA62 EXPERIMENTS AT CERN SPS

摘要

The branching fractions of K~± → π~±e~+e~? and K~± → π~±μ~+μ~? rare decays have been measured by the NA48/2 collaboration at CERN SPS. An improved upper limit has been set on the Lepton Number Violating decay K~± → π~μ~±μ~±. The branching ratio RK = Γ(K~±→ e~±ν)/K~±→ μ~±ν) has been measured by the NA62 collaboration at CERN SPS with an unprecedented accuracy, allowing a precise test of lepton flavour universality. The NA62 experiment is now undergoing a major upgrade in order to measure the branching fraction of the very rare K~± → π~±vv decay with a 10% precision.