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A bstract We present measurements of the branching fractions for the decays B → Kμ + μ − and B → Ke + e − , and their ratio ( R K ), using a data sample of 711 fb − 1 that contains 772 × 10 6 B B ¯ events. The data were collected at the ϒ(4 S ) resonance with the Belle detector at the KEKB asymmetric-energy e + e − collider. The ratio R K is measured in five bins of dilepton invariant-mass-squared ( q 2 ): q 2 ∈ (0 . 1 , 4 . 0) , (4 . 00 , 8 . 12) , (1 . 0 , 6 . 0), (10 . 2 , 12 . 8) and ( > 14 . 18) GeV 2 /c 4 , along with the whole q 2 region. The R K value for q 2 ∈ (1 . 0 , 6 . 0) GeV 2 /c 4 is 1.03 − 0.24 + 0.28 ± 0 . 01. The first and second uncertainties listed are statistical and systematic, respectively. All results for R K are consistent with Standard Model predictions. We also measure CP -averaged isospin asymmetries in the same q 2 bins. The results are consistent with a null asymmetry, with the largest difference of 2.6 standard deviations occurring for the q 2 ∈ (1 . 0 , 6 . 0) GeV 2 /c 4 bin in the mode with muon final states. The measured differential branching fractions, d ℬ /dq 2 , are consistent with theoretical predictions for charged B decays, while the corresponding values are below the expectations for neutral B decays. We have also searched for lepton-flavor-violating B → Kμ ± e ∓ decays and set 90% confidence-level upper limits on the branching fraction in the range of 10 − 8 for B + → K + μ ± e ∓ , and B 0 → K 0 μ ± e ∓ modes.

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 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.

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 Using the data samples of 102 million Υ(1 S ) and 158 million Υ(2 S ) events collected by the Belle detector, we search for a pentaquark state in the pJ/ψ final state from Υ(1 , 2 S ) inclusive decays. Here, the charge-conjugate is included. We observe clear pJ/ψ production in Υ(1 , 2 S ) decays and measure the branching fractions to be and . We also measure the cross section of inclusive pJ/ψ production in e + e − annihilation to be σ ( e + e − → pJ/ψ + anything ) = [108 ± 11( stat. ) ± 6( syst. )] fb at GeV using an 89 . 5 fb − 1 continuum data sample. There is no significant P c (4312) + , P c (4440) + or P c (4457) + signal found in the pJ/ψ final states in Υ(1 , 2 S ) inclusive decays. We determine the upper limits of to be at the 10 − 6 level.

We present a study of$$ {\\Xi}_c^0\\to {\\Xi}^0{\\pi}^0 $$Ξ c 0 → Ξ 0 π 0 ,$$ {\\Xi}_c^0\\to {\\Xi}^0\\eta $$Ξ c 0 → Ξ 0 η , and$$ {\\Xi}_c^0\\to {\\Xi}^0{\\eta}^{\\prime } $$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$$ {\\displaystyle \\begin{array}{c}\\mathcal{B}\\left({\\Xi}_c^0\\to {\\Xi}^0{\\pi}^0\\right)/\\mathcal{B}\\left({\\Xi}_c^0\\to {\\Xi}^{-}{\\pi}^{+}\\right)=0.48\\pm 0.02\\left(\\textrm{stat}\\right)\\pm 0.03\\left(\\textrm{syst}\\right),\\\ {}\\mathcal{B}\\left({\\Xi}_c^0\\to {\\Xi}^0\\eta \\right)/\\mathcal{B}\\left({\\Xi}_c^0\\to {\\Xi}^{-}{\\pi}^{+}\\right)=0.11\\pm 0.01\\left(\\textrm{stat}\\right)\\pm 0.01\\left(\\textrm{syst}\\right),\\\ {}\\mathcal{B}\\left({\\Xi}_c^0\\to {\\Xi}^0{\\eta}^{\\prime}\\right)/\\mathcal{B}\\left({\\Xi}_c^0\\to {\\Xi}^{-}{\\pi}^{+}\\right)=0.08\\pm 0.02\\left(\\textrm{stat}\\right)\\pm 0.01\\left(\\textrm{syst}\\right)\\end{array}} $$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,$$ \\mathcal{B}\\left({\\Xi}_c^0\\to {\\Xi}^{-}{\\pi}^{+}\\right) $$B Ξ c 0 → Ξ − π + , we obtain the following absolute branching fraction results$$ {\\displaystyle \\begin{array}{c}\\mathcal{B}\\left({\\Xi}_c^0\\to {\\Xi}^0{\\pi}^0\\right)=\\left(6.9\\pm 0.3\\left(\\textrm{stat}\\right)\\pm 0.5\\left(\\textrm{syst}\\right)\\pm 1.3\\left(\\operatorname{norm}\\right)\\right)\\times {10}^{-3},\\\ {}\\mathcal{B}\\left({\\Xi}_c^0\\to {\\Xi}^0\\eta \\right)=\\left(1.6\\pm 0.2\\left(\\textrm{stat}\\right)\\pm 0.2\\left(\\textrm{syst}\\right)\\pm 0.3\\left(\\operatorname{norm}\\right)\\right)\\times {10}^{-3},\\\ {}\\mathcal{B}\\left({\\varXi}_c^0\\to {\\Xi}^0{\\eta}^{\\prime}\\right)=\\left(1.2\\pm 0.3\\left(\\textrm{stat}\\right)\\pm 0.1\\left(\\textrm{syst}\\right)\\pm 0.2\\left(\\operatorname{norm}\\right)\\right)\\times {10}^{-3},\\end{array}} $$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$$ \\mathcal{B}\\left({\\Xi}_c^0\\to {\\Xi}^{-}{\\pi}^{+}\\right) $$B Ξ c 0 → Ξ − π + . The asymmetry parameter for$$ {\\Xi}_c^0\\to {\\Xi}^0{\\pi}^0 $$Ξ c 0 → Ξ 0 π 0 is measured to be$$ \\alpha \\left({\\Xi}_c^0\\to {\\Xi}^0{\\pi}^0\\right)=-0.90\\pm 0.15\\left(\\textrm{stat}\\right)\\pm 0.23\\left(\\textrm{syst}\\right) $$α Ξ c 0 → Ξ 0 π 0 = − 0.90 ± 0.15 stat ± 0.23 syst .

A bstract We present the analysis of two-particle angular correlations using coordinate systems defined with the conventional beam axis and the event thrust axis. We propose the latter as a good representation for the correlation structure interpretation in the e + e − collision system. The e + e − collisions to hadronic final states at center-of-mass energies of s = 10 . 52 GeV and 10.58 GeV are recorded by the Belle detector at KEKB. In this paper, results on the first dataset are supplementary to the previous Belle publication [ 1 ]. At the same time, the latter is the first two-particle correlation measurement at collision energy on the Υ (4 S ) resonance and is sensitive to its decay products. Measurements are reported as a function of the charged-particle multiplicity. Finally, a qualitative understanding of the correlation structure is discussed using a combination of Monte Carlo simulations and experimental data.

A bstract We report the measurement of the two-photon decay width of χ c 2 (1 P ) in two-photon processes at the Belle experiment. We analyze the process γγ → χ c 2 (1 P ) → J/ψγ , J/ψ → ℓ + ℓ − ( ℓ = e or μ ) using a data sample of 971 fb − 1 collected with the Belle detector at the KEKB e + e − collider. In this analysis, the product of the two-photon decay width of χ c 2 (1 P ) and the branching fraction is determined to be Γ γγ χ c 2 1 P B χ c 2 1 P → J / ψγ B J / ψ → ℓ + ℓ − = 14.8 ± 0.3 stat . ± 0.7 syst . eV, which corresponds to Γ γγ ( χ c 2 (1 P )) = 653 ± 13(stat.) ± 31(syst.) ± 17(B.R.) eV, where the third uncertainty is from B ( χ c 2 (1 P ) → J/ψγ ) and B ( J/ψ → ℓ + ℓ − ).

A bstract The first dedicated search for the η c 2 (1 D ) is carried out using the decays B + → η c 2 (1 D ) K + , B 0 → η c 2 (1 D ) K S 0 , B 0 → η c 2 (1 D ) π − K + , and B + → η c 2 (1 D ) π + K S 0 with η c 2 (1 D ) → h c γ . No significant signal is found. For the η c 2 (1 D ) mass range between 3795 and 3845 MeV /c 2 , the branching-fraction upper limits are determined to be ℬ( B + → η c 2 (1 D ) K + ) × ℬ( η c 2 (1 D ) → h c γ ) < 3 . 7 × 10 − 5 , ℬ( B 0 → η c 2 (1 D ) K 0 ) × ℬ( η c 2 (1 D ) → h c γ ) < 3 . 5 × 10 − 5 , ℬ( B 0 → η c 2 (1 D ) π − K + ) × ℬ( η c 2 (1 D ) → h c γ ) < 1 . 0 × 10 − 4 , and ℬ( B + → η c 2 (1 D ) π + K S 0 ) × ℬ( η c 2 (1 D ) → h c γ ) < 1 . 1 × 10 − 4 at 90% C.L. The analysis is based on the 711 fb − 1 data sample collected on the ϒ(4 S ) resonance by the Belle detector, which operated at the KEKB asymmetric-energy e + e − collider.

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 + .