Search for $B \rightarrow K \nu \bar{\nu}$ and other electroweak/radiative penguin processes at Belle II

Sumitted to PubDB: 2021-10-03

Category: Proceeding, Visibility: Public

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Authors	Simon Kurz
Date	Oct. 3, 2021
Belle II Number	BELLE2-CONF-PROC-2021-021
Abstract	This contribution summarizes the first results from searches for electroweak and radiative penguin processes at the \belletwo experiment installed at the SuperKEKB asymmetric energy electron-positron collider. The data sample considered by the analyses corresponds to an integrated luminosity of $63\invfb$ collected at the \Y4S resonance. A brief summary of a search for $\B \to X_s \gamma$ 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 \BKnn. 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 \BKnn of \limObs is set at the 90\% confidence level.