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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
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We search for the rare decay in a sample of electron-positron collisions at the resonance collected with the Belle II detector at the SuperKEKB collider. We use the inclusive properties of the accompanying meson in events to suppress background from other decays of the signal candidate and light-quark pair production. We validate the measurement with an auxiliary analysis based on a conventional hadronic reconstruction of the accompanying meson. For background suppression, we exploit distinct signal features using machine learning methods tuned with simulated data. The signal-reconstruction efficiency and background suppression are validated through various control channels. The branching fraction is extracted in a maximum likelihood fit. Our inclusive and hadronic analyses yield consistent results for the branching fraction of and , respectively. Combining the results, we determine the branching fraction of the decay to be , providing the first evidence for this decay at 3.5 standard deviations. The combined result is 2.7 standard deviations above the standard model expectation. Published by the American Physical Society2024more » « less
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We report a measurement of decay-time-dependent charge-parity ( ) asymmetries in decays. We use pairs collected at the resonance with the Belle II detector at the SuperKEKB asymmetric-energy electron-positron collider. We reconstruct 220 signal events and extract the -violating parameters and from a fit to the distribution of the decay-time difference between the two mesons. The resulting confidence region is consistent with previous measurements in and decays and with predictions based on the standard model. Published by the American Physical Society2024more » « less
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A<sc>bstract</sc> We report results from a study ofB±→ DK±decays followed byDdecaying to theCP-even final stateK+K−and CP-odd final state$$ {K}_S^0{\pi}^0 $$ , whereDis an admixture ofD0and$$ {\overline{D}}^0 $$ states. These decays are sensitive to the Cabibbo-Kobayashi-Maskawa unitarity-triangle angleϕ3. The results are based on a combined analysis of the final data set of 772×106$$ B\overline{B} $$ pairs collected by the Belle experiment and a data set of 198×106$$ B\overline{B} $$ pairs collected by the Belle II experiment, both in electron-positron collisions at the Υ(4S) resonance. We measure the CP asymmetries to be$$ \mathcal{A} $$ CP+= (+12.5±5.8±1.4)% and$$ \mathcal{A} $$ CP−= (−16.7±5.7±0.6)%, and the ratios of branching fractions to be$$ \mathcal{R} $$ CP+= 1.164±0.081±0.036 and$$ \mathcal{R} $$ CP−= 1.151±0.074±0.019. The first contribution to the uncertainties is statistical, and the second is systematic. The asymmetries$$ \mathcal{A} $$ CP+and$$ \mathcal{A} $$ CP−have similar magnitudes and opposite signs; their difference corresponds to 3.5 standard deviations. From these values we calculate 68.3% confidence intervals of (8.5°<ϕ3< 16.5°) or (84.5°<ϕ3< 95.5°) or (163.3°<ϕ3< 171.5°) and 0.321 <rB< 0.465.more » « less