Search for lepton-number- and baryon-number-violating tau decays at Belle

Abstract

We search for lepton-number- and baryon-number-violating decays ${\tau }^{-}\to \overline{p}{e}^{+}{e}^{-}$, $p{e}^{-}{e}^{-}$, $\overline{p}{e}^{+}{\mu }^{-}$, $\overline{p}{e}^{-}{\mu }^{+}$, $\overline{p}{\mu }^{+}{\mu }^{-}$, and $p{\mu }^{-}{\mu }^{-}$ using 921 fb${}^{-1}$ of data, equivalent to $(841\pm 12)\times 10^6$ ${\tau }^{+}{\tau }^{-}$ events, recorded with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. In the absence of a signal, $90\%$ confidence-level upper limits are set on the branching fractions of these decays in the range $(1.8$-$4.0)\times 10^{-8}$. We set the world's first limits on the first four channels and improve the existing limits by an order of magnitude for the last two channels.

Comments: 8 pages, 5 figures, 1 table