Search for Lepton and Baryon Number Violating tau- Decays into Lambda-bar pi- and Lambda pi-

TL;DR

This study searched for rare tau decays violating lepton and baryon number conservation into Lambda pi and Lambda-bar pi, setting upper limits on their branching fractions with no evidence of signal.

Contribution

First-ever search for tau decays into Lambda pi and Lambda-bar pi modes violating lepton and baryon number conservation, establishing new upper limits.

Findings

No evidence of the decay modes was observed.

Upper limits on branching fractions were set at 1.4×10^{-7} and 0.72×10^{-7}.

This is the first search for these specific decay modes.

Abstract

We have searched for tau lepton decays, tau- -> Lambda-bar pi- and tau- -> Lambda pi-, that simultaneously violate the conservation of the lepton and baryon number using a data sample of 154 fb^{-1} collected with the Belle detector at the KEKB e+e- asymmetric-energy collider. No evidence for a signal was found in either of the decay modes and we set the following upper limits for the branching fractions: B(tau^- -> Lambda-bar\pi-) < 1.4 * 10^{-7} and B(tau^- -> Lambda pi^-) < 0.72 * 10^{-7} at the 90% confidence level. This is the first search ever performed for these modes.