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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 + .

The Belle II experiment’s ability to identify particles critically affects the sensitivity of its measurements. We describe Belle II’s algorithms for identifying charged particles and evaluate their performance in separating pions, kaons, and protons using 426 fb - 1 of data collected at the energy-asymmetric e + e - collider SuperKEKB in 2019–2022 at center-of-mass energies at and near the mass of the Υ (4S).

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 .

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 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 report measurements of the absolute branching fractions , , and , where the latter is measured for the first time. The results are based on a 121.4 fb − 1 data sample collected at the Υ(10860) resonance by the Belle detector at the KEKB asymmetric-energy e + e − collider. We reconstruct one meson in events and measure yields of , D 0 , and D + mesons in the rest of the event. We obtain , , and , where the first uncertainty is statistical and the second is systematic. Averaging with previous Belle measurements gives and . For the production fraction at the Υ(10860), we find .

Abstract We report measurements of the absolute branching fractions$$\\mathcal{B}\\left({B}_{s}^{0}\\to {D}_{s}^{\\pm }X\\right)$$,$$\\mathcal{B}\\left({B}_{s}^{0}\\to {D}^{0}/{\\overline{D} }^{0}X\\right)$$, and$$\\mathcal{B}\\left({B}_{s}^{0}\\to {D}^{\\pm }X\\right)$$, where the latter is measured for the first time. The results are based on a 121.4 fb −1 data sample collected at the Υ(10860) resonance by the Belle detector at the KEKB asymmetric-energy e + e − collider. We reconstruct one$${B}_{s}^{0}$$meson in$${e}^{+}{e}^{-}\\to \\Upsilon\\left(10860\\right)\\to {B}_{s}^{*}{\\overline{B} }_{s}^{*}$$events and measure yields of$${D}_{s}^{+}$$, D 0, and D + mesons in the rest of the event. We obtain$$\\mathcal{B}\\left({B}_{s}^{0}\\to {D}_{s}^{\\pm }X\\right)=\\left(68.6\\pm 7.2\\pm 4.0\\right)\\%$$,$$\\mathcal{B}\\left({B}_{s}^{0}\\to {D}^{0}/{\\overline{D} }^{0}X\\right)=\\left(21.5\\pm 6.1\\pm 1.8\\right)\\%$$, and$$\\mathcal{B}\\left({B}_{s}^{0}\\to {D}^{\\pm }X\\right)=\\left(12.6\\pm 4.6\\pm 1.3\\right)\\%$$, where the first uncertainty is statistical and the second is systematic. Averaging with previous Belle measurements gives$$\\mathcal{B}\\left({B}_{s}^{0}\\to {D}_{s}^{\\pm }X\\right)=\\left(63.4\\pm 4.5\\pm 2.2\\right)\\%$$and$$\\mathcal{B}\\left({B}_{s}^{0}\\to {D}^{0}/{\\overline{D} }^{0}X\\right)=\\left(23.9\\pm 4.1\\pm 1.8\\right)\\%$$. For the$${B}_{s}^{0}$$production fraction at the Υ(10860), we find$${f}_{s}=\\left({21.4}_{-1.7}^{+1.5}\\right)\\%$$.

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$$ {\\Xi}_c^{+}\\to p{K}_S^0 $$Ξ c + → p K S 0 ,$$ {\\Xi}_c^{+}\\to \\Lambda {\\pi}^{+} $$Ξ c + → Λ π + , and$$ {\\Xi}_c^{+}\\to {\\Sigma}^0{\\pi}^{+} $$Ξ c + → Σ 0 π + are observed for the first time. The ratios of branching fractions of$$ {\\Xi}_c^{+}\\to p{K}_S^0 $$Ξ c + → p K S 0 ,$$ {\\Xi}_c^{+}\\to \\Lambda {\\pi}^{+} $$Ξ c + → Λ π + , and$$ {\\Xi}_c^{+}\\to {\\Sigma}^0{\\pi}^{+} $$Ξ c + → Σ 0 π + relative to that of$$ {\\Xi}_c^{+}\\to {\\Xi}^{-}{\\pi}^{+}{\\pi}^{+} $$Ξ c + → Ξ − π + π + are measured to be$$ {\\displaystyle \\begin{array}{c}\\frac{\\mathcal{B}\\left({\\Xi}_c^{+}\\to p{K}_S^0\\right)}{\\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Xi}^{-}{\\pi}^{+}{\\pi}^{+}\\right)}=\\left(2.47\\pm 0.16\\pm 0.07\\right)\\%,\\\ {}\\frac{\\mathcal{B}\\left({\\Xi}_c^{+}\\to \\Lambda {\\pi}^{+}\\right)}{\\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Xi}^{-}{\\pi}^{+}{\\pi}^{+}\\right)}=\\left(1.56\\pm 0.14\\pm 0.09\\right)\\%,\\\ {}\\frac{\\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Sigma}^0{\\pi}^{+}\\right)}{\\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Xi}^{-}{\\pi}^{+}{\\pi}^{+}\\right)}=\\left(4.13\\pm 0.26\\pm 0.22\\right)\\%.\\end{array}} $$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,$$ \\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Xi}^{-}{\\pi}^{+}{\\pi}^{+}\\right)=\\left(2.9\\pm 1.3\\right)\\% $$B Ξ c + → Ξ − π + π + = 2.9 ± 1.3 % , the absolute branching fractions are determined to be$$ {\\displaystyle \\begin{array}{c}\\mathcal{B}\\left({\\Xi}_c^{+}\\to p{K}_S^0\\right)=\\left(7.16\\pm 0.46\\pm 0.20\\pm 3.21\\right)\\times {10}^{-4},\\\ {}\\mathcal{B}\\left({\\Xi}_c^{+}\\to \\Lambda {\\pi}^{+}\\right)=\\left(4.52\\pm 0.41\\pm 0.26\\pm 2.03\\right)\\times {10}^{-4},\\\ {}\\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Sigma}^0{\\pi}^{+}\\right)=\\left(1.20\\pm 0.08\\pm 0.07\\pm 0.54\\right)\\times {10}^{-3}.\\end{array}} $$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$$ \\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Xi}^{-}{\\pi}^{+}{\\pi}^{+}\\right) $$B Ξ c + → Ξ − π + π + .

Abstract 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.

Abstract 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$$ {\\Xi}_c^{+}\\to p{K}_S^0 $$, Ξ c + → Λ π +$$ {\\Xi}_c^{+}\\to \\Lambda {\\pi}^{+} $$, and Ξ c + → Σ 0 π +$$ {\\Xi}_c^{+}\\to {\\Sigma}^0{\\pi}^{+} $$are observed for the first time. The ratios of branching fractions of Ξ c + → p K S 0$$ {\\Xi}_c^{+}\\to p{K}_S^0 $$, Ξ c + → Λ π +$$ {\\Xi}_c^{+}\\to \\Lambda {\\pi}^{+} $$, and Ξ c + → Σ 0 π +$$ {\\Xi}_c^{+}\\to {\\Sigma}^0{\\pi}^{+} $$relative to that of Ξ c + → Ξ − π + π +$$ {\\Xi}_c^{+}\\to {\\Xi}^{-}{\\pi}^{+}{\\pi}^{+} $$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 % .$$ {\\displaystyle \\begin{array}{c}\\frac{\\mathcal{B}\\left({\\Xi}_c^{+}\\to p{K}_S^0\\right)}{\\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Xi}^{-}{\\pi}^{+}{\\pi}^{+}\\right)}=\\left(2.47\\pm 0.16\\pm 0.07\\right)\\%,\\\ {}\\frac{\\mathcal{B}\\left({\\Xi}_c^{+}\\to \\Lambda {\\pi}^{+}\\right)}{\\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Xi}^{-}{\\pi}^{+}{\\pi}^{+}\\right)}=\\left(1.56\\pm 0.14\\pm 0.09\\right)\\%,\\\ {}\\frac{\\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Sigma}^0{\\pi}^{+}\\right)}{\\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Xi}^{-}{\\pi}^{+}{\\pi}^{+}\\right)}=\\left(4.13\\pm 0.26\\pm 0.22\\right)\\%.\\end{array}} $$Multiplying these values by the branching fraction of the normalization channel, B Ξ c + → Ξ − π + π + = 2.9 ± 1.3 %$$ \\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Xi}^{-}{\\pi}^{+}{\\pi}^{+}\\right)=\\left(2.9\\pm 1.3\\right)\\% $$, 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 .$$ {\\displaystyle \\begin{array}{c}\\mathcal{B}\\left({\\Xi}_c^{+}\\to p{K}_S^0\\right)=\\left(7.16\\pm 0.46\\pm 0.20\\pm 3.21\\right)\\times {10}^{-4},\\\ {}\\mathcal{B}\\left({\\Xi}_c^{+}\\to \\Lambda {\\pi}^{+}\\right)=\\left(4.52\\pm 0.41\\pm 0.26\\pm 2.03\\right)\\times {10}^{-4},\\\ {}\\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Sigma}^0{\\pi}^{+}\\right)=\\left(1.20\\pm 0.08\\pm 0.07\\pm 0.54\\right)\\times {10}^{-3}.\\end{array}} $$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 +$$ \\mathcal{B}\\left({\\Xi}_c^{+}\\to {\\Xi}^{-}{\\pi}^{+}{\\pi}^{+}\\right) $$.