Search for charged-lepton flavor violation in Υ(2S) → ℓ∓τ± (ℓ = e, μ) decays at Belle

A bstract We report a search for the charged-lepton flavor violation in Υ(2 S ) → ℓ ∓ τ ± ( ℓ = e, μ ) decays using a 25 fb − 1 Υ(2 S ) sample collected by the Belle detector at the KEKB e + e − asymmetric-energy collider. We find no evidence for a signal and set upper limits on the branching fractions ( B B ) at 90% confidence level. We obtain the most stringent upper limits: B B (Υ(2 S ) → μ ∓ τ ± ) < 0 . 23 × 10 − 6 and B B (Υ(2 S ) → e ∓ τ ± ) < 1 . 12 × 10 − 6 .