Measurement of $B^+\to\tau^+\nu_\tau$ branching fraction with a hadronic tagging method at Belle II

Abstract We present a measurement of the branching fraction of $B^+\to\tau^+\nu_\tau$ decays using $(387\pm6)\times 10^6$ $\Upsilon(4S)$ collected between 2019 and 2022 with the Belle II detector at the SuperKEKB $e^+e^-$ collider. We reconstruct the accompanying $B^-$ meson using the hadronic tagging method, while $B^+\to\tau^+\nu_\tau$ candidates are identified in the recoil. We find evidence for $B^+\to\tau^+\nu_\tau$ decays at 3.0 standard deviations, including systematic uncertainties. The measured branching fraction is $\mathcal{B}(B^+\to\tau^+\nu_\tau) = [1.24 \pm 0.41 (\text{stat.}) \pm 0.19 (\text{syst.})] \times 10^{-4}$.
Tags Run 1
Working group Semileptonic and Missing Energy Decay
Principal authors @  Michele Aversano, Guglielmo De Nardo, Giovanni Gaudino, Toru Iijima, Mario Merola
Reference Phys.Rev.D 112, 072002 (2025), DOI: 10.1103/dcwd-5tg4
Document BELLE2-PUB-DRAFT-2024-013
Links arXiv:2502.04885, Inspire, PRD
Bibtex 
@article{Belle-II:2025ruy,
    author = "Adachi, I. and others",
    collaboration = "Belle-II",
    title = "{Measurement of B+{\textrightarrow}{\ensuremath{\tau}}+{\ensuremath{\nu}}{\ensuremath{\tau}} branching fraction with a hadronic tagging method at Belle II}",
    eprint = "2502.04885",
    archivePrefix = "arXiv",
    primaryClass = "hep-ex",
    reportNumber = "Belle II preprint 2024-033, KEK preprint 2024-48",
    doi = "10.1103/dcwd-5tg4",
    journal = "Phys. Rev. D",
    volume = "112",
    number = "7",
    pages = "072002",
    year = "2025"
}