A test of lepton flavour universality with a measurement of $R(D^{(*)})$ using semileptonic B tagging and leptonic $\tau$ decays

Abstract We report the measurement of the branching fractions $\mathcal{R}(D^{(*)}) = \frac{\mathcal{B}(\overline{B} \to D^{(*)} \tau \bar{\nu}_\tau)}{\mathcal{B}(\overline{B} \to D^{(*)} \ell \bar{\nu}_\ell)}$ with $\ell$ denoting either an electron or a muon. This measurement tests the universality of the charged-current weak interaction and utilises 364fb$^{-1}$ of integrated luminosity of electron-positron collision data collected with the Belle~II detector. Signal candidates are reconstructed in collision events in which one of the $B$ mesons in the $\Upsilon(4S) \to B\overline B$ decay is fully reconstructed in semileptonic modes, and the $\tau$ is reconstructed using leptonic decays.
Tags Run 1
Working group Semileptonic and Missing Energy Decay
Principal authors @  Florian Bernlochner, Jochen Dingfelder, Peter Lewis, Alina Manthei, Markus Prim
Reference Phys.Rev.D 112, 032010 (2025), DOI: 10.1103/fmn3-h8fy
Document BELLE2-PUB-DRAFT-2024-014
Links arXiv:2504.11220, Inspire, PRD
Bibtex 
@article{Belle-II:2025yjp,
    author = "Adachi, I. and others",
    collaboration = "Belle-II",
    title = "{Test of lepton flavor universality with measurements of R(D+) and R(D*+) using semileptonic B tagging at the Belle II experiment}",
    eprint = "2504.11220",
    archivePrefix = "arXiv",
    primaryClass = "hep-ex",
    reportNumber = "Belle II Preprint 2025-011, KEK Preprint 2025-9",
    doi = "10.1103/fmn3-h8fy",
    journal = "Phys. Rev. D",
    volume = "112",
    number = "3",
    pages = "032010",
    year = "2025"
}