Search for lepton flavor-violating decay modes B0 → K*0τ±ℓ∓ (ℓ = e, μ) with hadronic B-tagging at Belle and Belle II

A bstract We present the results of a search for the charged-lepton-flavor violating decays B 0 → K *0 τ ± ℓ ∓ , where ℓ ∓ is either an electron or a muon. The results are based on 365 fb − 1 and 711 fb − 1 datasets collected with the Belle II and Belle detectors, respectively. We use an exclusive hadronic B -tagging technique, and search for a signal decay in the system recoiling against a fully reconstructed B meson. We find no evidence for B 0 → K *0 τ ± ℓ ∓ decays and set upper limits on the branching fractions in the range of (2.9–6.4)×10 − 5 at 90% confidence level.