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

TL;DR

This study searches for charged-lepton-flavor violation in $ ext{chi}_{bJ}(1P)$ decays using a large dataset, finding no signals but setting stringent upper limits on branching fractions and Wilson coefficients.

Contribution

First search for charged-lepton-flavor violation in $ ext{chi}_{bJ}(1P)$ decays, providing new upper limits and constraints on scalar operator Wilson coefficients.

Findings

No significant signals observed.

Upper limits on branching fractions at $10^{-6}$ to $10^{-5}$.

Constraints on Wilson coefficients for scalar operators.

Abstract

We report the first searches for charged-lepton-flavor violation in decays of $\chi_{bJ}(1P)$ ($J=0, 1,$ and $2$) to a pair of charged leptons using 158 million $\Upsilon(2S)$ decays collected with the Belle detector in $e^+e^-$ collisions at the KEKB collider. No significant signal is observed, and we set upper limits on the branching fractions for $\chi_{bJ}(1P)$ decays to $e^\pm\mu^\mp$ at the level of $10^{-6}$ and to $e^\pm\tau^\mp$ or $\mu^\pm\tau^\mp$ at the level of $10^{-5}$. Limits on $\chi_{b0}(1P)$ decays are translated into bounds on the corresponding Wilson coefficients of scalar operators that mediate charged-lepton-flavor violation.