Search for lepton flavor and lepton number violating τ decays into a lepton and two charged mesons

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±), τ−→ℓ−h+h′− and τ−→ℓ+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)×10−8 for τ→ehh′, and (3.3-16)×10−8 for τ→μhh′ processes. These results improve upon previously published upper limits by factors between 1.6 to 8.8.