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A bstract We report a measurement of the electric dipole moment of the τ lepton ( dτ ) using an 833 fb − 1 data sample collected near the Υ(4 S ) resonance, with the Belle detector at the KEKB asymmetric-energy e + e − collider. Using an optimal observable method, we obtain the real and imaginary parts of d τ as Re( d τ ) = ( − 0 . 62 ± 0 . 63) × 10 − 17 e cm and Im( d τ ) = ( − 0 . 40 ± 0 . 32) × 10 − 17 e cm, respectively. These results are consistent with null electric dipole moment at the present level of experimental sensitivity and improve the sensitivity by about a factor of three.

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 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.

A bstract We report a search for the lepton-flavor-violating decays τ ± → ℓ ± α ( ℓ = e , μ ), where α is an undetected spin-0 particle, such as an axion-like particle using 736 × 10 6 tau lepton pairs collected by the Belle detector at the KEKB asymmetric-energy e + e − collider. We find no evidence of signal and obtain the most stringent upper limits on the branching fractions at 95% confidence level: ( τ ± → e ± α ) < (0.4–6.4) × 10 − 4 and ( τ ± → μ ± α ) < (0.2–3.5) × 10 − 4 at 95% confidence level for an α mass in the range 0.0 ≤ m α ≤ 1.6 GeV/ c 2 .

A bstract We present a search for the lepton-flavor-violating decays B s 0 → ℓ ∓ τ ± , where ℓ = e, μ , using the full data sample of 121 fb − 1 collected at the Υ(5 S ) resonance with the Belle detector at the KEKB asymmetric-energy e + e − collider. We use B s 0 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 B ( B s 0 → e ∓ τ ± ) < 14 × 10 − 4 and 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.

A bstract We present the first measurement of the branching fraction of the singly Cabibbo-suppressed (SCS) decay Λ c + → pη ′ with η ′ → ηπ + π − , using a data sample corresponding to an integrated luminosity of 981 fb − 1 , collected by the Belle detector at the KEKB e + e − asymmetric-energy collider. A significant Λ c + → pη ′ signal is observed for the first time with a signal significance of 5.4 σ . The relative branching fraction with respect to the normalization mode Λ c + → pK − π + is measured to be B Λ c + → pη ′ B Λ c + → pK − π + = 7.54 ± 1.32 ± 0.73 × 10 − 3 , where the uncertainties are statistical and systematic, respectively. Using the world-average value of B Λ c + → pK − π + = (6 . 28 ± 0 . 32) × 10 − 2 , we obtain B Λ c + → pη ′ = 4.73 ± 0.82 ± 0.46 ± 0.24 × 10 − 4 , where the uncertainties are statistical, systematic, and from B Λ c + → pK − π + , respectively.

A bstract We report a new measurement of the e + e − → ϒ( nS ) π + π − ( n = 1 , 2 , 3) cross sections at energies from 10 . 52 to 11 . 02 GeV using data collected with the Belle detector at the KEKB asymmetric-energy e + e − collider. We observe a new structure in the energy dependence of the cross sections; if described by a Breit-Wigner function its mass and width are found to be M = 10752.7 ± 5.9 − 1.1 + 0.7 MeV / c 2 and Γ = 35.5 − 11.3 − 3.3 + 17.6 + 3.9 MeV, where the first error is statistical and the second is systematic. The global significance of the new structure including systematic uncertainty is 5.2 standard deviations. We also find evidence for the e + e − → ϒ (1 S ) π + π − process at the energy 10 . 52 GeV, which is below the B B ¯ threshold.

A bstract We present a study of Ξ c 0 → Ξ 0 π 0 , Ξ c 0 → Ξ 0 η , and Ξ c 0 → Ξ 0 η ′ decays using the Belle and Belle II data samples, which have integrated luminosities of 980 fb − 1 and 426 fb − 1 , respectively. We measure the following relative branching fractions B Ξ c 0 → Ξ 0 π 0 / B Ξ c 0 → Ξ − π + = 0.48 ± 0.02 stat ± 0.03 syst , B Ξ c 0 → Ξ 0 η / B Ξ c 0 → Ξ − π + = 0.11 ± 0.01 stat ± 0.01 syst , B Ξ c 0 → Ξ 0 η ′ / B Ξ c 0 → Ξ − π + = 0.08 ± 0.02 stat ± 0.01 syst for the first time, where the uncertainties are statistical (stat) and systematic (syst). By multiplying by the branching fraction of the normalization mode, B Ξ c 0 → Ξ − π + , we obtain the following absolute branching fraction results B Ξ c 0 → Ξ 0 π 0 = 6.9 ± 0.3 stat ± 0.5 syst ± 1.3 norm × 10 − 3 , B Ξ c 0 → Ξ 0 η = 1.6 ± 0.2 stat ± 0.2 syst ± 0.3 norm × 10 − 3 , B Ξ c 0 → Ξ 0 η ′ = 1.2 ± 0.3 stat ± 0.1 syst ± 0.2 norm × 10 − 3 , where the third uncertainties are from B Ξ c 0 → Ξ − π + . The asymmetry parameter for Ξ c 0 → Ξ 0 π 0 is measured to be α Ξ c 0 → Ξ 0 π 0 = − 0.90 ± 0.15 stat ± 0.23 syst .

A bstract We present a measurement of the ratio R μ = B τ − → μ − ν ¯ μ ν τ / B τ − → e − ν ¯ e ν τ of branching fractions B of the τ lepton decaying to muons or electrons using data collected with the Belle II detector at the SuperKEKB e + e − collider. The sample has an integrated luminosity of 362 ± 2 fb − 1 at a centre-of-mass energy of 10.58 GeV. Using an optimised event selection, a binned maximum likelihood fit is performed using the momentum spectra of the electron and muon candidates. The result, R μ = 0.9675 ± 0.0007 ± 0.0036, where the first uncertainty is statistical and the second is systematic, is the most precise to date. It provides a stringent test of the light-lepton universality, translating to a ratio of the couplings of the muon and electron to the W boson in τ decays of 0.9974 ± 0.0019, in agreement with the standard model expectation of unity.

A bstract We report results from a study of B ± → DK ± decays followed by D decaying to the CP -even final state K + K − and CP-odd final state K S 0 π 0 , where D is an admixture of D 0 and D ¯ 0 states. These decays are sensitive to the Cabibbo-Kobayashi-Maskawa unitarity-triangle angle ϕ 3 . The results are based on a combined analysis of the final data set of 772 × 10 6 B B ¯ pairs collected by the Belle experiment and a data set of 198 × 10 6 B B ¯ pairs collected by the Belle II experiment, both in electron-positron collisions at the Υ(4 S ) resonance. We measure the CP asymmetries to be A CP + = (+12.5 ± 5.8 ± 1.4)% and A CP− = ( − 16.7 ± 5.7 ± 0.6)%, and the ratios of branching fractions to be R CP + = 1.164 ± 0.081 ± 0.036 and R CP− = 1.151 ± 0.074 ± 0.019. The first contribution to the uncertainties is statistical, and the second is systematic. The asymmetries A CP + and 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 ° < ϕ 3 < 16.5 ° ) or (84.5 ° < ϕ 3 < 95.5 ° ) or (163.3 ° < ϕ 3 < 171.5 ° ) and 0.321 < r B < 0.465.

A bstract We present measurements of B → K * (892) γ decays using 365 fb − 1 of data collected from 2019 to 2022 by the Belle II experiment at the SuperKEKB asymmetric-energy e + e − collider. The data sample contains (387 ± 6) × 10 6 Υ(4 S ) events. We measure branching fractions ( ) and CP asymmetries ( ) for both B 0 → K *0 γ and B + → K *+ γ decays. The difference in CP asymmetries ( ) and the isospin asymmetry (∆ 0+ ) between these neutral and charged channels are also measured. We obtain the following branching fractions and CP asymmetries: , , , and . The measured difference in CP asymmetries is , and the measured isospin asymmetry is ∆ 0+ = (+4.8 ± 2.0 ± 1.8)%. The first uncertainties listed are statistical and the second are systematic. These results are consistent with world-average values and theory predictions.