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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.

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 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 the results of a search for charged-lepton-flavor violating decaysτ ⁻→ ℓ⁻K_(s)⁰, 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 modesτ ⁻→ e⁻K_(S)⁰andτ ⁻→ μ ⁻K_(S)⁰, respectively. These are the most stringent upper limits to date.

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.