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The Belle II experiment, being constructed at the KEK laboratory in Japan, is a substantial upgrade of the Belle detector. The construction of the SuperKEKB accelerator, which is the upgrade of the KEKB accelerator, has been just completed. It aims to collect 50 times more data than the existing B-Factory samples beginning in 2018. Belle II is uniquely positioned to study the so-called XYZ particles: heavy exotic hadrons consisting of more than three quarks. First discovered by Belle, the number of these particles is in the dozens now, which implies the emergence of a new category within quantum chromodynamics. This talk will present the capabilities of Belle II to explore exotic and conventional bottomonium physics. There will be a particular focus on the physics reach of the first data, where opportunities exist to make an immediate impact on the field.

We present measurements ofB → K^(*)(892)γdecays using365 \\rm fb⁻¹of data collected from 2019 to 2022 by the Belle II experiment at the SuperKEKB asymmetric-energye⁺e⁻collider. The data sample contains(387 ± 6) × 10⁶Υ(4S)events. We measure branching fractions ( 𝓑 ) andC\\!{P}{}{a}symmetries ( 𝓐_(C\\!P) ) for bothB⁰→ K^(*0)γandB⁺→ K^(*+)γdecays. The difference inC\\!{P}{}{a}symmetries ( Δ𝓐_(C\\!P) ) and the isospin asymmetry ( Δ₀₊ ) between these neutral and charged channels are also measured. We obtain the following branching fractions andC\\!{P}{}{a}symmetries:𝓑 (B⁰ → K^(*0)γ) = (4.14 ± 0.10 ± 0.11 ) × 10⁻⁵ ,𝓑 (B⁺ → K^(*+)γ) = (4.04 ± 0.13 ^(+0.13)_(-0.15) )× 10⁻⁵ ,𝓐_(C\\!P) (B⁰ → K^(*0)γ) = (-3.3 ± 2.3 ± 0.4 )% , and𝓐_(C\\!P) (B⁺ → K^(*+)γ) = (-0.7 ± 2.9 ± 0.5 )% . The measured difference inC\\!{P}{}{a}symmetries isΔ𝓐_(C\\!P) = (+2.6 ± 3.8 ± 0.6 )% , and the measured isospin asymmetry isΔ₀₊ = (+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.

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 ⁻¹and 711 fb ⁻¹datasets 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 ⁻⁵at 90% confidence level. 19 pages, 4 figures

We report measurements of the absolute branching fractions𝓑(B_(s)⁰ → D_(s)^(±) X) ,𝓑(B_(s)⁰ → D⁰/D̄⁰ X) , and𝓑(B_(s)⁰ → D^(±) X) , where the latter is measured for the first time. The results are based on a 121.4 fb ⁻¹data sample collected at theΥ(10860)resonance by the Belle detector at the KEKB asymmetric-energye⁺ e⁻collider. We reconstruct oneB_(s)⁰meson ine⁺e⁻ → Υ(10860) → B_(s)^(*) B̄_(s)^(*)events and measure yields ofD_(s)⁺ ,D⁰ , andD⁺mesons in the rest of the event. We obtain𝓑(B_(s)⁰ → D_(s)^(±) X) = (68.6 ± 7.2 ± 4.0)% ,𝓑(B_(s)⁰ → D⁰/D̄⁰ X) = (21.5 ± 6.1 ± 1.8)% , and𝓑(B_(s)⁰ → D^(±) X) = (12.6 ± 4.6 ± 1.3)% , where the first uncertainty is statistical and the second is systematic. Averaging with previous Belle measurements gives𝓑(B_(s)⁰ → D_(s)^(±) X) = (63.4 ± 4.5 ± 2.2)%and𝓑(B_(s)⁰ → D⁰/D̄⁰ X) = (23.9 ± 4.1 ± 1.8)% . For theB_(s)⁰production fraction at theΥ(10860) , we findf_(s) = (21.4^(+1.5)_(-1.7))% .

We perform the first search for$C\\!P$violation in${D_{(s)}^{+}\\to{}K_{S}^{0}K^{-}\\pi^{+}\\pi^{+}}$decays. We use a combined data set from the Belle and Belle II experiments, which study$e^+e^-$collisions at center-of-mass energies at or near the$\\Upsilon(4S)$resonance. We use 980 fb $^{-1}$of data from Belle and 428 fb $^{-1}$of data from Belle~II. We measure six$C\\!P$ -violating asymmetries that are based on triple products and quadruple products of the momenta of final-state particles, and also the particles' helicity angles. We obtain a precision at the level of 0.5% for$D^+\\to{}K_{S}^{0}K^{-}\\pi^{+}\\pi^{+}$decays, and better than 0.3% for$D^+_{s}\\to{}K_{S}^{0}K^{-}\\pi^{+}\\pi^{+}$decays. No evidence of$C\\!P$violation is found. Our results for the triple-product asymmetries are the most precise to date for singly-Cabibbo-suppressed$D^+$decays. Our results for the other asymmetries are the first such measurements performed for charm decays. 21 pages, 10 figures

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 + .

We report measurements of thee⁺e⁻ → BB̄ ,BB̄^(*) , andB^(*)B̄^(*)cross sections at four energies, 10653, 10701, 10746 and 10805 MeV, using data collected by the Belle II experiment. We reconstruct oneBmeson in a large number of hadronic final states and use its momentum to identify the production process. In the first2-5MeV aboveB^(*)B̄^(*)threshold, thee⁺e⁻ → B^(*)B̄^(*)cross section increases rapidly. This may indicate the presence of a pole close to the threshold.

A bstract 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 .

We report results from a study ofB^(±) → DK^(±)decays followed byDdecaying toCP eigenstates, whereDindicates aD⁰orD̄⁰meson. These decays are sensitive to the Cabibbo-Kobayashi-Maskawa unitarity-triangle angleφ₃ . The results are based on a combined analysis of the final data set of772 × 10⁶ BB̄pairs collected by the Belle experiment and a data set of198 × 10⁶ BB̄pairs collected by the Belle II experiment, both in electron-positron collisions at theΥ(4S)resonance. We measure theCPasymmetries 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 asymmetries𝓐_(CP +)and𝓐_(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°<φ₃<16.5° ) or ( 84.5°<φ₃<95.5° ) or ( 163.3°<φ₃<171.5° ) and0.321

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