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A<sc>bstract</sc> We report a search for the charged-lepton flavor violation in Υ(2S) →ℓ∓τ±(ℓ=e, μ) decays using a 25 fb−1Υ(2S) sample collected by the Belle detector at the KEKBe+e−asymmetric-energy collider. We find no evidence for a signal and set upper limits on the branching fractions ($$ \mathcal{B} $$ ) at 90% confidence level. We obtain the most stringent upper limits:$$ \mathcal{B} $$ (Υ(2S)→ μ∓τ±)<0.23×10−6and$$ \mathcal{B} $$ (Υ(2S)→ e∓τ±)<1.12×10−6.more » « less
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We measure the branching fraction of the decay using data collected with the Belle II detector. The data contain 387 million pairs produced in collisions at the resonance. We reconstruct decays from an analysis of the distributions of the energy and the helicity angle. We determine the branching fraction to be , in agreement with previous results. Our measurement improves the relative precision of the world average by more than a factor of two. Published by the American Physical Society2024more » « less
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A<sc>bstract</sc> We present a search for the lepton-flavor-violating decays$$ {B}_s^0 $$ →ℓ∓τ±, whereℓ=e, μ, using the full data sample of 121 fb−1collected at the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energye+e−collider. We use$$ {B}_s^0{\overline{B}}_s^0 $$ events in which one$$ {B}_s^0 $$ meson is reconstructed in a semileptonic decay mode and the other in the signal mode. We find no evidence for$$ {B}_s^0 $$ → ℓ∓τ±decays and set upper limits on their branching fractions at 90% confidence level as$$ \mathcal{B} $$ ($$ {B}_s^0 $$ → e∓τ±)<14×10−4and$$ \mathcal{B} $$ ($$ {B}_s^0 $$ → μ∓τ±)<7.3×10−4. Our result represents the first upper limit on the$$ {B}_s^0 $$ → e∓τ±decay rate.more » « less
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A bstract Charged-lepton-flavor-violation is predicted in several new physics scenarios. We update the analysis of τ lepton decays into a light charged lepton ( ℓ = e ± or μ ± ) and a vector meson ( V 0 = ρ 0 , ϕ , ω , K *0 , or $$ \overline{K} $$ K ¯ *0 ) using 980 fb − 1 of data collected with the Belle detector at the KEKB collider. No significant excess of such signal events is observed, and thus 90% credibility level upper limits are set on the τ → ℓV 0 branching fractions in the range of (1.7–4 . 3) × 10 − 8 . These limits are improved by 30% on average from the previous results.more » « less