Measurement of the very rare $K^+ \rightarrow \pi^+ \nu \overline{\nu}$ decay at the NA62 experiment at CERN

The NA62 experiment reports the branching ratio measurement $BR(K^+\to\pi^+\nu\bar\nu)$ at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016-2018. This provides evidence for the very rare $K^+\to\pi^+\nu\bar\nu$ decay, observed with a significance of $3.4\sigma$. The experiment achieves a single event sensitivity of $(0.839\pm0.054)\times10^{-11}$, corresponding to 10.0 events assuming the Standard Model branching ratio of $(8.4\pm1.0)\times10^{-11}$. The result represents the most accurate measurement achieved so far of this ultra-rare decay. Future prospects and plans for data taking from 2021 will also be presented.