Search for the Lepton-Flavor-Violating Leptonic $B^0\to {\mu }^{\pm }{\tau }^{\mp }$ and $B^0\to e^{\pm }{\tau }^{\mp }$

We have searched a sample of $9.6\times {10}^6$ $B\overline{B}$ events for the lepton-flavor-violating leptonic $B$ decays, $B^0\to {\mu }^{\pm }{\tau }^{\mp }$ and $B^0\to e^{\pm }{\tau }^{\mp }$. The $\tau$ lepton was detected through the decay modes $\tau \to \ell \nu \overline{\nu }$, where $\ell =e,\mu$. There is no indication of a signal, and we obtain the 90% confidence level upper limits $\mathcal{B}(B^0\to {\mu }^{\pm }{\tau }^{\mp })<3.8\times {10}^{-5}$ and $\mathcal{B}(B^0\to e^{\pm }{\tau }^{\mp })<1.3\times {10}^{-4}$.

Figure 1

(a) $\mathrm{N}{\mathrm{N}}_{\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{t}}$, (b) ${\mathrm{N}\mathrm{N}}_{B\overline{B}}$, (c) $\Delta M_{\tau }$, and (d) $\Delta M_{\tau ,\Delta E=0}$ distributions, for the comparison of $B\overline{B}$ Monte Carlo calculations (solid line) vs off-resonance-subtracted on-resonance data (points) in the ${\overrightarrow{p}}_{\ell }$ sideband region, for the ($\mu$, $e$) mode. The distributions of signal Monte Carlo calculations are also displayed with a dashed line.

Figure 2

(a) $\mathrm{N}{\mathrm{N}}_{\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{t}}$, (b) ${\mathrm{N}\mathrm{N}}_{B\overline{B}}$, (c) $\Delta M_{\tau }$, and (d) $\Delta M_{\tau ,\Delta E=0}$ distributions, for the comparison of continuum Monte Carlo ($e^{+}{e}^{-}\to q\overline{q},q=u,d,s,c$: histogram) calculations vs off-vresonance data (points) in the ${\overrightarrow{p}}_{\ell }$ sideband region, for the ($\mu$, $e$) mode.