Search for Lepton-Flavor-Violating and Lepton-Number-Violating tau to lhh' Decay Modes

TL;DR

This study searches for rare tau decays violating lepton flavor and number, setting new upper limits on their branching fractions, thereby constraining new physics models beyond the Standard Model.

Contribution

First search for tau to lhh' decays using 854 fb^{-1} data, providing improved upper limits on branching fractions by factors of about 1.8.

Findings

Upper limits on branching fractions range from 2.0 to 8.4 x 10^{-8}

Results improve previous limits by approximately 1.8 times

No evidence of lepton-flavor- or lepton-number-violating tau decays found

Abstract

We search for lepton-flavor-violating and lepton-number-violating tau decays into a lepton (l = electron or muon) and two charged mesons (h, h' = pion or Kaon) using 854 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We obtain 90% confidence level upper limits on the tau to lhh' branching fractions in the range (2.0-8.4)*10^{-8}. These results improve upon our previously published upper limits by factors of about 1.8 on average.