NA48 results

Measured decay rates of $K^± \to e^± π^0 ν_e$ and $K^± \to µ^± π^0 ν_µ$ normalized to $K^± \to π^± π^0$ are presented. These measurements are based on K ± decays collected in a dedicated run in 2003 by the NA48/2 experiment at CERN. Using the PDG 2006 average for the $K^± \to π^± π^0$ normalization mode, the results are found to be larger than the current values given by the PDG 2006 and lead to a larger magnitude of the $|V_{us}|$ CKM element than previously accepted. When combined with the latest PDG 2006 value of $|V_{ud}|$, the result is in agreement with unitarity of the CKM matrix. The ratio $R_K = Γ(K^± \to e^± ν)/Γ(K^± \to µ^± ν)$ is calculated with very high precision within the Standard Model (SM), but corrections due to the presence of New Physics could be as high as 3%. The data obtained by the NA48/2 experiment in two years of data taking at the CERN SPS accelerator has been analyzed. The obtained result for $R_K$ is two times more precise than the world average but is still insufficient to probe the existence of physics beyond the Standard Model. The status of the analysis of the data taken in 2007, aimed for a sub-percent precision of $R_K$ , will be summarized.