New Result on $K^+ \rightarrow \pi^+ \nu \overline{\nu}$ from the NA62 Experiment

The NA62 experiment at the CERN SPS is designed to measure the branching ratio of the $K^+ \rightarrow \pi^+ \nu \overline{\nu}$ with a decay-in-flight technique and took data in 2016–2018. The statistics collected in 2017 allows NA62 to achieve the best up–to–date single event sensitivity for $K^+ \rightarrow \pi^+ \nu \overline{\nu}$ corresponding to more than 2 Standard Model $K^+ \rightarrow \pi^+ \nu \overline{\nu}$ expected events. The analysis of the 2017 data has revealed 2 candidate $K^+ \rightarrow \pi^+ \nu \overline{\nu}$ events, while 1.5 background were expected. Together with the candidate found on the 2016 data, this result leads to 1.85 × 10$^{-10}$ as preliminary upper limit at 90% C.L. on the branching ratio of the $K^+ \rightarrow \pi^+ \nu \overline{\nu}$ decay. The 2017 data also allow NA62 to achieve the best up–to–date sensitivity on the search for the $\pi ^{0}$ → invisible decay.