A stringent test of μ − e universality in $K\to l\nu$ decays by NA62 at CERN

New interest has arisen in measuring the ratio $R_K$ = $K_{e}2/K_{/mu}2$, as recent high-intensity kaon experiments arc able to largely improve the precision. With ~150000 collected Ke2 decays, the NA62 experiment has increased the world $K_{e}2$ sample by an order of magnitude, allowing a stringent test of $\mu - e$ lepton universality. Here, we describe the experiment and summarize the status of the analysis based on ~40 % of the total data sample taken in 2007.