Search of New Physics with Kaon decays at NA62

NA62 is a fixed target experiment at the CERN SPS aiming at the search for new phenomena beyond the Standard Model (SM) by measuring two of the theoretically most clean processes in kaon decays. Two phases can be distinguished in the NA62 physics programme. During the current short term phase (data taking completed in years 2007-8) we are studying the ratio RK = G(K!ene(g)) G(K!mnm (g)) of leptonic decay rates, which provides a golden probe for testing the structure of the weak interactions. In the second phase (long term) we will then focus on the measurement of the branching ratio of the very rare kaon decay K+ ! p+n ¯ n aiming at collecting O(100) K+ !p+n ¯ n events with 10% background in two years of data taking. In this paper we first summarize the status of the RK analysis, based on 40% of the 2007 NA62 data sample, and discuss the preliminary result RK = (2:500 0:016)10􀀀5, which breaks for the first time the 1% error level and is consistent with the Standard Model. A status report of the longer term project, recently approved at CERN, will then follow, including the current R&D programme and future perspectives for the K+ !p+n ¯ n measurement, for which data taking will start in year 2012.