Speaker
Description
The $K^{+}\rightarrow\pi^{+}\nu\bar{\nu}$ decay is a golden mode for flavour physics. Its branching ratio is predicted with high precision by the Standard Model to be less than $10^{-10}$, and this decay mode is highly sensitive to indirect effects of new physics up to the highest mass scales. A new measurement of the $K^{+}\rightarrow\pi^{+}\nu\bar{\nu}$ decay by the NA62 experiment at the CERN SPS is presented, using data collected in 2021 and 2022. This new data-set was collected after modifications to the beamline and detectors and at a higher instantaneous beam intensity with respect to the previous 2016--2018 data taking. Using the NA62 data-set from 2016--2022, a new measurement of $\mathcal{B}(K^{+}\rightarrow\pi^{+}\nu\bar{\nu}) = \left(13.0^{+ 3.3}_{- 2.9} \right)\times10^{-11}$ is reported, and for the first time the $K^{+}\rightarrow\pi^{+}\nu\bar{\nu}$ decay is observed with a significance exceeding $5\sigma$.
