Evidence for B + → K + ν ν ¯ decays

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doi:10.1103/PhysRevD.109.112006

Title: Evidence for $B^{+} \to K^{+} ν \bar{ν}$ decays

Journal Article · 06 June 2024 · Physical Review. D.

DOI: https://doi.org/10.1103/PhysRevD.109.112006 · OSTI ID:2473478

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We search for the rare decay $B^{+} \to K^{+} ν \bar{ν}$ in a $362 {fb}^{- 1}$ sample of electron-positron collisions at the $ϒ (4 S)$ resonance collected with the Belle II detector at the SuperKEKB collider. We use the inclusive properties of the accompanying $B$ meson in $ϒ (4 S) \to B \bar{B}$ events to suppress background from other decays of the signal $B$ candidate and light-quark pair production. We validate the measurement with an auxiliary analysis based on a conventional hadronic reconstruction of the accompanying $B$ meson. For background suppression, we exploit distinct signal features using machine learning methods tuned with simulated data. The signal-reconstruction efficiency and background suppression are validated through various control channels. The branching fraction is extracted in a maximum likelihood fit. Our inclusive and hadronic analyses yield consistent results for the $B^{+} \to K^{+} ν \bar{ν}$ branching fraction of $[2.7 \pm 0.5 (stat) \pm 0.5 (syst)] \times 10^{- 5}$ and $[{1.1}_{- 0.8}^{+ 0.9} (stat)_{- 0.5}^{+ 0.8} (syst)] \times 10^{- 5}$ , respectively. Combining the results, we determine the branching fraction of the decay $B^{+} \to K^{+} ν \bar{ν}$ to be $[2.3 \pm 0.5 (stat)_{- 0.4}^{+ 0.5} (syst)] \times 10^{- 5}$ , providing the first evidence for this decay at 3.5 standard deviations. The combined result is 2.7 standard deviations above the standard model expectation. Published by the American Physical Society 2024

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Sponsoring Organization:: USDOE

Grant/Contract Number:: AC06-76RL01830; AC06-76RL01830

OSTI ID:: 2473478

Journal Information:: Physical Review. D., Journal Name: Physical Review. D. Journal Issue: 11 Vol. 109; ISSN PRVDAQ; ISSN 2470-0010

Publisher:: American Physical SocietyCopyright Statement

Country of Publication:: United States

Language:: English

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