Search for lepton-flavor and lepton-number-violating τ→ℓhh′ decay modes

We search for lepton-flavor and lepton-number-violating τ decays into a lepton (l= electron or muon) and two charged mesons ( h , h ′ = π ± or K ± ) 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 τ → l h h ′ 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.