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

Abstract We report a search for the charged-lepton flavor violation in Υ(2S) → ℓ ∓ τ ± (ℓ = e, μ) decays using a 25 fb −1 Υ(2S) 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 $$ \mathcal{B} $$ ) at 90% confidence level. We obtain the most stringent upper limits: B $$ \mathcal{B} $$ (Υ(2S) → μ ∓ τ ± ) < 0.23 × 10 −6 and B $$ \mathcal{B} $$ (Υ(2S) → e ∓ τ ± ) < 1.12 × 10 −6.