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

Abstract A search for the flavor-changing neutral-current decay $B^{+}\to K^{+}\nu\bar{\nu}$ is performed at the Belle II experiment at the SuperKEKB asymmetric energy electron-positron collider. The results are based on a data sample corresponding to an integrated luminosity of $63\,\mbox{fb}^{-1}$ collected at the $\Upsilon{(4S)}$ resonance and a sample of $9\,\mbox{fb}^{-1}$ collected at an energy $60\mathrm{\,Me\kern -0.1em V}$ below the resonance. A novel measurement method is employed, which exploits topological properties of the $B^{+}\to K^{+}\nu\bar{\nu}$ decay that differ from both generic bottom-meson decays and light-quark pair production. This inclusive tagging approach offers a higher signal efficiency compared to previous searches. No significant signal is observed. An upper limit on the branching fraction of $B^{+}\to K^{+}\nu\bar{\nu}$ of $4.1 \times 10^{-5}$ is set at the 90% confidence level.
Tags
Working group Radiative and Electroweak Penguin
Principal authors @  Filippo Dattola, Alexander Glazov, Simon Kurz, Cyrille Praz, Slavomira Stefkova
Reference Phys.Rev.Lett. 127, 181802 (2021), DOI: 10.1103/PhysRevLett.127.181802
Document BELLE2-PUB-PH-2021-004
Links arXiv:2104.12624, Inspire, PRL
Bibtex 
@article{Belle-II:2021rof,
    author = "Abudin{\'e}n, F. and others",
    collaboration = "Belle-II",
    title = "{Search for B+{\textrightarrow}K+{\ensuremath{\nu}}{\ensuremath{\nu}}{\textasciimacron} Decays Using an Inclusive Tagging Method at Belle II}",
    eprint = "2104.12624",
    archivePrefix = "arXiv",
    primaryClass = "hep-ex",
    reportNumber = "Belle II Preprint 2021-001, KEK Preprint 2020-45",
    doi = "10.1103/PhysRevLett.127.181802",
    journal = "Phys. Rev. Lett.",
    volume = "127",
    number = "18",
    pages = "181802",
    year = "2021"
}