Measurement of the branching ratio of the $K^{+}\rightarrowπ^{+}ν\barν$ decay

Abstract

The NA62 experiment has measured the branching ratio of the rare decay $K^+\toπ^+ν\barν$ using data collected in 2023 and 2024 at the CERN SPS, obtaining ${\rm B}_{\rm 2023-2024}(K^+\toπ^+ν\barν) = \left(7.2^{+2.3}_{-2.1}\right)\times10^{-11}$. With results from data collected between 2016 and 2022, the analysis gives ${\rm B}_{\rm 2016-2024}(K^+\toπ^+ν\barν) = \left(9.6^{+1.9}_{-1.8}\right)\times10^{-11}$, corresponding to a relative precision of $20\%$. This value is consistent with Standard Model predictions.