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  • Evidence for ▫$B^+ \to K^+ \nu \bar{\nu}$▫ decays [Elektronski vir]
    Adachi, Ichiro ...
    We search for the rare decay 𝐵+ →𝐾+⁢𝜈⁢ ¯ 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)→𝐵⁢ ¯ 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+ →𝐾+⁢𝜈⁢ ¯ 𝜈 branching fraction of [2.7±0.5⁢(stat)±0.5⁢(syst)] ×10−5 and [1.1+0.9 −0.8⁢(stat)+0.8 −0.5⁢(syst)] ×10−5, respectively. Combining the results, we determine the branching fraction of the decay 𝐵+ →𝐾+⁢𝜈⁢ ¯ 𝜈 to be [2.3±0.5⁢(stat)+0.5 −0.4⁢(syst)] ×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.
    Source: Physical review. D. [Elektronski vir]. - ISSN 2470-0029 (Vol. 109, 112006, Jun. 2024, str. 112006-1-112006-29)
    Type of material - e-article ; adult, serious
    Publish date - 2024
    Language - english
    COBISS.SI-ID - 252623363

    Link(s):

    https://journals.aps.org/prd/abstract/10.1103/PhysRevD.109.112006
    DOI

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