Search for charged lepton flavor violation in $\chi_{bJ}(1P)$ meson decays

Abstract We report the first searches for lepton-flavor violation in decays of the $\chi_{bJ}(1P)$ ($J$ = 0, 1, or 2) using 158 million $\Upsilon(2S)$ decays collected by the Belle detector in $e^+e^-$ collision at a center-of-mass energy corresponding to the mass of the $\Upsilon(2S)$ resonance. We do not observe any significant signals and so determine the upper limits on the branching fractions at 90\% confidence for lepton flavor violating decays of the $\chi_{bJ}(1P)$ mesons, at order $10^{-6}$ for decay to $e^{\pm}\mu^{\mp}$ and $10^{-6}$ to $10^{-5}$ for decay to $e^{\pm}\tau^{\mp}$ or $\mu^{\pm}\tau^{\mp}$. We translate the limits on $\chi_{b0}(1P)$ decay into bounds on Wilson coefficients for lepton-flavor-violating scalar operators.
Tags Belle
Working group Quarkonium
Principal authors @  Swagato Banerjee, Vishal Bhardwaj, Sourav Patra, Karim Trabelsi
Reference Phys.Rev.Lett. 137, 071803 (2026), DOI: 10.1103/1rj5-2wvr
Document BELLE2-PUB-PH-2025-041
Links arXiv:2603.10818, Inspire, PRL
Bibtex 
@article{Belle:2026ebk,
    author = "Abumusabh, M. and others",
    collaboration = "Belle, Belle-II",
    title = "{Searches for Charged-Lepton-Flavor Violation in {\ensuremath{\chi}}bJ(1P) Decays}",
    eprint = "2603.10818",
    archivePrefix = "arXiv",
    primaryClass = "hep-ex",
    reportNumber = "Belle{\textasciitilde}II Preprint 2026-005, KEK Preprint 2026-1",
    doi = "10.1103/1rj5-2wvr",
    journal = "Phys. Rev. Lett.",
    volume = "137",
    number = "7",
    pages = "071803",
    year = "2026"
}