PubDB | BELLE2-PUB-PH-2025-041

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	submitted to PRL
Links	arXiv:2603.10818,

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.

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