Observation of the $K^{+}\to {\pi }^{+}\nu \bar{\nu }$ decay and measurement of its branching ratio

Abstract

A measurement of the $K^{+}\to {\pi }^{+}\nu \bar{\nu }$ decay by the NA62 experiment at the CERN SPS is presented, using data collected in 2021 and 2022. This dataset was recorded, after modifications to the beamline and detectors, at a higher instantaneous beam intensity with respect to the 2016--2018 data taking. Combining NA62 data collected in 2016--2022, a measurement of $B(K^{+}\to {\pi }^{+}\nu \bar{\nu })=\left(13.0_{-3.0}^{+3.3}\right)\times 10^{-11}$ is reported. With $51$ signal candidates observed and an expected background of $18_{-2}^{+3}$ events, $B(K^{+}\to {\pi }^{+}\nu \bar{\nu })$ becomes the smallest branching ratio measured with a signal significance above $5\sigma$.

References in corpus (7)

• Two-Loop Electroweak Corrections for the K -> pi nu anti-nu Decays
• Improved estimates of rare K decay matrix-elements from Kl3 decays
• Probing Lepton Flavour Universality with $K\to \pi \nu \bar{\nu }$ decays
• Disentangling new physics in $K\to \pi \bar{\nu }\nu$ and $B\to K(K^{\ast })\bar{\nu }\nu$ observables
• Anatomy of kaon decays and prospects for lepton flavour universality violation
• Probing lepton number violating interactions in rare kaon decays
• Correlating New Physics Effects in Semileptonic $\Delta C=1$ and $\Delta S=1$ Processes

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• Dark Matter emission at Belle II and NA62 in Minimal Flavor Violation framework