In-flight Search for $K^+ \rightarrow \pi^+ \nu \overline{\nu}$: First NA62 Results

In this paper the prospects to make a precise measurement of the $K^+ \rightarrow \pi^+ \nu \overline{\nu}$ decay using a new kaon decay in-flight technique are reviewed. A preliminary result based on data collected in 2016 yielded one candidate event, compatible with the Standard Model prediction. Assuming that the event is background, an upper limit of $1.4 \times 10^{−9}$ (95% CL) has been placed. NA62 is currently taking data: it is expected that with the full data sample recorded before the CERN long shutdown 2 (LS2), the experiment will have about 20 SM events.