PoS - Proceedings of Science
Volume 398 - The European Physical Society Conference on High Energy Physics (EPS-HEP2021) - T08: Flavour Physics and CP Violation
Search for $B \rightarrow K \nu \bar{\nu}$ and other electroweak/radiative penguin processes at Belle II
S. Kurz* and  On behalf of the BELLE II collaboration
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Pre-published on: January 12, 2022
Published on: May 12, 2022
This contribution summarizes the first results from searches for electroweak and radiative penguin processes at the Belle II experiment installed at the SuperKEKB asymmetric energy electron-positron collider. The data sample considered by the analyses corresponds to an integrated luminosity of $63\,\text{fb}^{-1}$ collected at the $\Upsilon(4S)$ resonance. A brief summary of a search for $B \rightarrow X_s \gamma$ decays is given. This flavor-changing neutral-current decay is sensitive to many Standard Model extensions. An excess is clearly visible in the expected region. The second result is a study of $B^{\pm}\to K^{\pm} \ell^+ \ell^-$ decays. This analysis will provide an independent measurement to shed more light onto the recently observed deviations from the Standard Model expectations. A preliminary measurement of the $B^{\pm}\to K^{\pm} \ell^+ \ell^-$ signal yield is discussed. The main topic of this contribution is a search for the flavor-changing neutral-current decay $B \rightarrow K \nu \bar{\nu}$. A novel measurement method is developed, which exploits topological and kinematic properties of the decay that differ from both other $B$-meson decays and light-quark pair-production. This multivariate approach offers a significantly higher signal efficiency than the techniques used in previous publications. No signal is observed and an upper limit on the branching fraction of $B \rightarrow K \nu \bar{\nu}$ of $4.1\times10^{−5}$ is set at the $90\%$ confidence level.
DOI: https://doi.org/10.22323/1.398.0554
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