Search for Lepton Flavor and Lepton Number Violating tau Decays into a Lepton and Two Charged Mesons

TL;DR

This study searches for rare tau decays violating lepton flavor and number, setting new upper limits on their branching fractions using Belle detector data, thus constraining new physics models.

Contribution

First comprehensive search for tau decays into a lepton and two charged mesons, providing the most stringent upper limits to date.

Findings

Upper limits on branching fractions range from 4.4 to 16 x 10^{-8}.

Results improve previous limits by factors of 1.6 to 8.8.

No evidence of lepton flavor or number violation observed.

Abstract

We search for lepton flavor and lepton number violating tau decays into a lepton (ell = electron or muon) and two charged mesons (h,h' = pi^\pm or K^\pm), tau- -> ell-h+h'- and tau- -> ell+h-h'-, using 671 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. We obtain 90% C.L. upper limits on the branching fractions in the range (4.4-8.8)x10^{-8} for tau -> ehh', and (3.3-16)x10^{-8} for tau -> muhh' processes. These results improve upon previously published upper limits by factors between 1.6 to 8.8.