Search for lepton flavor violating decay $B^0 \rightarrow K^{*0} \tau \ell$ using the Belle and Belle II data sample

Abstract We present the results of a search for the charged-lepton-flavor violating decays $B^{0} \to K^{*0} \tau^{\pm}\ell^{\mp}$, where $\ell^{\mp}$ is either an electron or a muon. The results are based on 365 fb$^{−1}$ and 711 fb$^{−1}$ datasets collected with the Belle II and Belle detectors, respectively. We use an exclusive hadronic $B$-tagging technique, and search for the signal decay in the system recoiling against the fully reconstructed $B$ meson. We find no evidence for $B^{0} \to K^{*0} \tau^{\pm}\ell^{\mp}$ decays and set upper limits on the branching fractions in the range of (2.9–6.4)$\times 10^{-5}$ at 90% confidence level.
Tags Run 1 Belle
Working group Radiative and Electroweak Penguin
Principal authors @  Valerio Bertacchi, Clotilde Lemettais, Giampiero Mancinelli, Justine Serrano
Reference JHEP 08, 184 (2025), DOI: 10.1007/JHEP08(2025)184
Document BELLE2-PUB-PH-2025-012
Links arXiv:2505.08418, Inspire, JHEP
Bibtex 
@article{Belle:2025sgv,
    author = "Adachi, I. and others",
    collaboration = "Belle, Belle-II",
    title = "{Search for lepton flavor-violating decay modes B$^{0}${\textrightarrow} K$^{*0}${\ensuremath{\tau}}$^{±}${\ensuremath{\ell}}$^{∓}$ ({\ensuremath{\ell}} = e, {\ensuremath{\mu}}) with hadronic B-tagging at Belle and Belle II}",
    eprint = "2505.08418",
    archivePrefix = "arXiv",
    primaryClass = "hep-ex",
    reportNumber = "Belle II preprint: 2025-014, KEK preprint: 2025-13",
    doi = "10.1007/JHEP08(2025)184",
    journal = "JHEP",
    volume = "08",
    pages = "184",
    year = "2025"
}