Search for $B^{+}\to K^{+}\nu \bar{\nu }$ decays with an inclusive tagging method at the Belle II experiment

Abstract

This contribution illustrates a new search for the flavor-changing neutral-current decay $B^{+}\to K^{+}\nu \bar{\nu }$ performed by the Belle II experiment at the SuperKEKB asymmetric-energy electron-positron collider. In this study, a sample corresponding to an integrated luminosity of $63{\mathrm{fb}}^{-1}$ collected at the $\mathrm{{\rm Y}}(4S)$ resonance and an additional sample of $9{\mathrm{fb}}^{-1}$ collected at an energy $60\mathrm{MeV}$ below the resonance are used. A novel technique, based on an inclusive tagging method and exploiting the topological features of the $B^{+}\to K^{+}\nu \bar{\nu }$ decay, is employed and it provides a higher signal efficiency with respect to the methods used in the previous searches. No significant signal is observed. An upper limit of $4.1\times 10^{-5}$ is set on the $B^{+}\to K^{+}\nu \bar{\nu }$ branching fraction at the $90\%$ confidence level.

Contribution to the 2021 EW session of the 55th Rencontres de Moriond

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