New measurement of $K^{+} \rightarrow \pi^{+}\nu\bar{\nu}$ branching ratio at the NA62 experiment

The $K^{+}\rightarrow\pi^{+}\nu\bar{\nu}$ decay is a golden mode for flavour physics. Its branching ratio ($B$) is predicted with high precision by the Standard Model to be less than $10^{-10}$, and the decay is highly sensitive to new physics up to the highest mass scales. A new measurement of $B(K^{+}\rightarrow\pi^{+}\nu\bar{\nu})$ by the NA62 experiment at the CERN SPS is presented, using data collected in 2021--2022.The measurement $B(K^{+}\rightarrow\pi^{+}\nu\bar{\nu}) = \left(13.0^{+ 3.3}_{-3.0} \right)\times10^{-11} $ with the combined datasets from 2016--2022 is reported, and for the first time the $K^{+}\rightarrow\pi^{+}\nu\bar{\nu}$ decay is observed with a significance exceeding $5\sigma$.