Search for Lepton and Baryon Number Violating tau^- Decays into \bar{p}gamma, \bar{p}pi^0, \bar{Lambda}pi^-, and Lambda pi^-

TL;DR

This study searched for lepton and baryon number violating tau decays into specific hadronic final states, setting new upper limits on their branching fractions with no signals observed.

Contribution

First to search for these specific tau decays violating lepton and baryon number, establishing the most stringent upper limits to date.

Findings

No signals found in the searched decay modes.

Upper limits on branching fractions were set, improving previous limits significantly.

First searches ever performed for tau^- -> mbda pi^- and tau^- -> Lambda pi^- decays.

Abstract

We have searched for decays that violate both lepton and baryon number using data collected by the Belle detector at the KEKB asymmetric e^+e^- collider. No signals are found in tau^- -> \bar{p} gamma, tau^- -> \bar{p} pi^0, tau^- -> \bar{Lambda} pi^-, and tau^- -> Lambda pi^- and we set upper limits on the branching fractions of B(tau^- -> \bar{p}gamma) < 3.0*10^{-7}, B(tau^- -> \bar{p}pi^0) < 6.5*10^{-7}, B(tau^- -> \bar{Lambda}pi^-) < 1.3*10^{-7}, and B(tau^- -> Lambda pi^-) < 0.70*10^{-7} at the 90% confidence level. The former two results improve the previous limits by a factor of 12 and 23, respectively, while the latter two are the first searches ever performed.