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

Abstract

We report the first searches for charged-lepton-flavor violation in decays of $χ_{bJ}(1P)$ ($J=0, 1,$ and $2$) to a pair of charged leptons using 158 million $Υ(2S)$ 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 $χ_{bJ}(1P)$ decays to $e^\pmμ^\mp$ at the level of $10^{-6}$ and to $e^\pmτ^\mp$ or $μ^\pmτ^\mp$ at the level of $10^{-5}$. Limits on $χ_{b0}(1P)$ decays are translated into bounds on the corresponding Wilson coefficients of scalar operators that mediate charged-lepton-flavor violation.

Figures (4)

• Figure 1: $M^{{\rm recoil}}_{\rm \gamma_1}$ distributions for $e^+e^-\to\gamma\gamma e^+ e^-$ (top) and $e^+e^-\to\gamma\gamma \mu^+ \mu^-$ (bottom) overlaid with fit results.
• Figure 2: $M^{{\rm recoil}}_{\rm \gamma_1}$ distribution for $e^+e^-\to\gamma e^\pm \mu^\mp$ candidates. The $\chi_{b1}(1P)$ component is too small to be visible.
• Figure 3: Fit projections of $M^{{\rm recoil}}_{\rm \gamma_1}$ (left) and $M^{{\rm recoil}}_{\rm \gamma_1\ell_1}$ (right) for $e^+e^-\to\gamma e^\pm \tau^\mp$ (top row) $e^+e^-\to\gamma \mu^\pm \tau^\mp$ (bottom row).
• Figure 4: Upper limits at the 90% confidence level on Wilson coefficients of scalar operators that mediate CLFV.