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A bstract Using data samples of 983.0 fb − 1 and 427.9 fb − 1 accumulated with the Belle and Belle II detectors operating at the KEKB and SuperKEKB asymmetric-energy e + e − colliders, singly Cabibbo-suppressed decays Ξ c + → p K S 0 , Ξ c + → Λ π + , and Ξ c + → Σ 0 π + are observed for the first time. The ratios of branching fractions of Ξ c + → p K S 0 , Ξ c + → Λ π + , and Ξ c + → Σ 0 π + relative to that of Ξ c + → Ξ − π + π + are measured to be B Ξ c + → p K S 0 B Ξ c + → Ξ − π + π + = 2.47 ± 0.16 ± 0.07 % , B Ξ c + → Λ π + B Ξ c + → Ξ − π + π + = 1.56 ± 0.14 ± 0.09 % , B Ξ c + → Σ 0 π + B Ξ c + → Ξ − π + π + = 4.13 ± 0.26 ± 0.22 % . Multiplying these values by the branching fraction of the normalization channel, B Ξ c + → Ξ − π + π + = 2.9 ± 1.3 % , the absolute branching fractions are determined to be B Ξ c + → p K S 0 = 7.16 ± 0.46 ± 0.20 ± 3.21 × 10 − 4 , B Ξ c + → Λ π + = 4.52 ± 0.41 ± 0.26 ± 2.03 × 10 − 4 , B Ξ c + → Σ 0 π + = 1.20 ± 0.08 ± 0.07 ± 0.54 × 10 − 3 . The first and second uncertainties above are statistical and systematic, respectively, while the third ones arise from the uncertainty in B Ξ c + → Ξ − π + π + .

A bstract We study the processes χ bJ ω and χ bJ ( π + π − π 0 ) non −ω ( J = 0, 1, 2) at center-of-mass energies from 10.73 to 11.02 GeV using a 142 . 5 fb − 1 data sample collected with the Belle detector at the KEKB asymmetric-energy e + e − collider; and at GeV using a 19 . 8 fb − 1 sample collected with Belle II at SuperKEKB. We find that the Υ(10753) state decays into χ bJ ω but not into χ bJ ( π + π − π 0 ) non −ω , while the Υ(10860) state, in contrast, decays into χ bJ ( π + π − π 0 ) non −ω but not into χ bJ ω . The mass and width of the Υ(10753) state are measured to be (10756 . 1 ± 3 . 4(stat . ) ± 2 . 7(syst . )) MeV/ c 2 and (32 . 2 ± 11 . 3(stat . ) ± 14 . 9(syst . )) MeV. The products of the partial width to e + e − and branching fractions for Υ(10753) → χ b 1 ω and Υ(10753) → χ b 2 ω are (1 . 57 ± 0 . 27(stat . ) ± 0 . 22(syst . )) eV and (1 . 39 ± 0 . 41(stat . ) ± 0 . 33(syst . )) eV.

We present a measurement of the time-dependent CP asymmetry in$${B}^{0}\\to {K}_{\\text{S}}^{0}{\\pi }^{+}{\\pi }^{-}\\gamma $$decays using a data set of 365 fb − 1 recorded by the Belle II experiment and the final data set of 711 fb − 1 recorded by the Belle experiment at the Υ(4S) resonance. The direct and mixing-induced time-dependent CP violation parameters C and S are determined along with two additional quantities, S + and S − , defined in the two halves of the$${m}^{2}\\left({K}_{\\text{S}}^{0}{\\pi }^{+}\\right)-{m}^{2}\\left({K}_{\\text{S}}^{0}{\\pi }^{-}\\right)$$plane. The measured values are C = − 0 . 17 ± 0 . 09 ± 0 . 04, S = − 0 . 29 ± 0 . 11 ± 0 . 05, S + = −0 . 57 ± 0 . 23 ± 0 . 10 and S − = 0 . 31 ± 0 . 24 ± 0 . 05, where the first uncertainty is statistical and the second systematic.

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.

A bstract We present a measurement of the time-dependent CP asymmetry in decays using a data set of 365 fb − 1 recorded by the Belle II experiment and the final data set of 711 fb − 1 recorded by the Belle experiment at the Υ(4S) resonance. The direct and mixing-induced time-dependent CP violation parameters C and S are determined along with two additional quantities, S + and S − , defined in the two halves of the plane. The measured values are C = − 0 . 17 ± 0 . 09 ± 0 . 04, S = − 0 . 29 ± 0 . 11 ± 0 . 05, S + = −0 . 57 ± 0 . 23 ± 0 . 10 and S − = 0 . 31 ± 0 . 24 ± 0 . 05, where the first uncertainty is statistical and the second systematic.

A bstract We present the result of a search for the charged-lepton-flavor violating decays τ − → e ∓ ℓ ± ℓ − , where ℓ is a muon or an electron, using a data sample with an integrated luminosity of 428 fb − 1 recorded by the Belle II experiment at the SuperKEKB e + e − collider. The selection of e + e − → τ + τ − events containing a signal candidate is based on an inclusive-tagging reconstruction and on a boosted decision tree to suppress background. Upper limits on the branching fractions between 1.3 and 2.5 × 10 − 8 are set at the 90% confidence level. These results are the most stringent bounds to date for four of the modes.

A bstract We report a search for an axion-like particle a in B → K (*) a decays using data collected with the Belle detector at the KEKB asymmetric-energy electron-positron collider. The search is based on a 711 fb − 1 data sample collected at the Υ(4 S ) resonance energy, corresponding to a sample of 772 × 10 6 Υ(4 S ) events. In this study, we search for the decay of the axion-like particle into a pair of photons, a → γγ . We scan the two-photon invariant mass in the range 0 . 16 GeV–4 . 50 GeV for the K modes and 0 . 16 GeV–4 . 20 GeV for the K * modes. No significant signal is observed in any of the modes, and 90% confidence level upper limits are established on the coupling to the W boson, g aW , as a function of a mass. The limits range from 3 × 10 − 6 GeV − 1 to 3 × 10 − 5 GeV − 1 , improving the current constraints on g aW by a factor of two over the most stringent previous experimental results.

A bstract We present the results of a search for charged-lepton-flavor violating decays , where ℓ − is either an electron or a muon. We combine e + e − data samples recorded by the Belle II experiment at the SuperKEKB collider (428 fb − 1 ) with samples recorded by the Belle experiment at the KEKB collider (980 fb − 1 ) to obtain a sample of 1.3 billion e + e − → τ + τ − events. We observe 0 and 1 events and set 90% confidence level upper limits of 0 . 8 × 10 − 8 and 1 . 2 × 10 − 8 on the branching fractions of the decay modes and , respectively. These are the most stringent upper limits to date.

Using 983.0\\rm{fb}{⁻¹}{}and 427.9\\rm{fb}{⁻¹}{}data samples collected with the Belle and Belle II detectors at the KEKB and SuperKEKB asymmetric energye⁺e⁻colliders, respectively, we present studies of the Cabibbo-favoredΞ_(c)⁺decaysΞ_(c)⁺→ Σ⁺K_(S)⁰andΞ_(c)⁺→ Ξ⁰π⁺ , and the singly Cabibbo-suppressed decayΞ_(c)⁺→ Ξ⁰K⁺ . The ratios of branching fractions ofΞ_(c)⁺→ Σ⁺K_(S)⁰andΞ_(c)⁺→ Ξ⁰K⁺relative to that ofΞ_(c)⁺\\toΞ{⁻}{π}{⁺}π⁺are measured for the first time, while the ratio𝓑(Ξ_(c)⁺\\toΞ{⁰}{π}{⁺})/𝓑(Ξ_(c)⁺\\toΞ{⁻}{π}{⁺}π⁺) is also determined and improved by an order of magnitude in precision. The measured branching fraction ratios are((𝓑(Ξ_(𝓬)⁺ → Σ⁺𝓚_(𝓢)⁰))/(𝓑(Ξ_(𝓬)⁺→ Ξ⁻π⁺π⁺)))= 0.067 ± 0.007 ± 0.003 ,((𝓑(Ξ_(𝓬)⁺ → Ξ⁰π⁺))/(𝓑(Ξ_(𝓬)⁺→ Ξ⁻π⁺π⁺))) = 0.251 ± 0.005 ± 0.010 ,((𝓑(Ξ_(𝓬)⁺ → Ξ⁰𝓚⁺))/(𝓑(Ξ_(𝓬)⁺→ Ξ⁻π⁺π⁺))) = 0.017 ± 0.003 ± 0.001 . Additionally, the ratio𝓑(Ξ_(c)⁺\\toΞ{⁰}{K}{⁺})/𝓑(Ξ_(c)⁺\\toΞ{⁰}{π}{⁺})is measured to be 0.068 ± 0.010 ± 0.004 . Here, the first and second uncertainties are statistical and systematic, respectively. Multiplying the ratios by the branching fraction of the normalization mode,𝓑(Ξ_(c)⁺\\toΞ{⁻}{π}{⁺}π⁺)= (2.9± 1.3)% , we obtain the following absolute branching fractions𝓑(Ξ_(c)⁺\\toΣ{⁺}{K}{⁰}_(S)) = (0.194 ± 0.021 ± 0.009 ± 0.087 )% ,𝓑(Ξ_(c)⁺\\toΞ{⁰}{π}{⁺}) = (0.728 ± 0.014 ± 0.027 ± 0.326 )% ,𝓑(Ξ_(c)⁺\\toΞ{⁰}{K}{⁺}) = (0.049 ± 0.007 ± 0.003 ± 0.022 )% .

A bstract Using 983.0 fb − 1 and 427.9 fb − 1 data samples collected with the Belle and Belle II detectors at the KEKB and SuperKEKB asymmetric energy e + e − colliders, respectively, we present studies of the Cabibbo-favored decays and , and the singly Cabibbo-suppressed decay . The ratios of branching fractions of and relative to that of are measured for the first time, while the ratio is also determined and improved by an order of magnitude in precision. The measured branching fraction ratios are Additionally, the ratio is measured to be 0 . 068 ± 0 . 010 ± 0 . 004. Here, the first and second uncertainties are statistical and systematic, respectively. Multiplying the ratios by the branching fraction of the normalization mode, , we obtain the following absolute branching fractions where the third uncertainties are from .