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We report on new flavor tagging algorithms developed to determine the quark-flavor content of bottom ( ) mesons at Belle II. The algorithms provide essential inputs for measurements of quark-flavor mixing and charge-parity violation. We validate and evaluate the performance of the algorithms using hadronic decays with flavor-specific final states reconstructed in a data set corresponding to an integrated luminosity of 62.8 fb-1, collected at the resonance with the Belle II detector at the SuperKEKB collider. We measure the total effective tagging efficiency to be εeff=(30.0±1.2(stat)±0.4(syst))%for a category-based algorithm and εeff=(28.8±1.2(stat)±0.4(syst))%for a deep-learning-based algorithm.

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.

A bstract We report a determination of the CKM angle ϕ 3 , also known as γ , from a combination of measurements using samples of up to 711 fb − 1 from the Belle experiment and up to 362 fb − 1 from the Belle II experiment. We combine results from analyses of B + → DK + , B + → Dπ + , and B + → D * K + decays, where D is an admixture of D 0 and D ¯ 0 mesons, in a likelihood fit to obtain ϕ 3 = (75.2 ± 7.6) ° . We also briefly discuss the interpretation of this result.

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.

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 measurements of B → K * (892) γ decays using 365 fb − 1 of data collected from 2019 to 2022 by the Belle II experiment at the SuperKEKB asymmetric-energy e + e − collider. The data sample contains (387 ± 6) × 10 6 Υ(4 S ) events. We measure branching fractions ( ) and CP asymmetries ( ) for both B 0 → K *0 γ and B + → K *+ γ decays. The difference in CP asymmetries ( ) and the isospin asymmetry (∆ 0+ ) between these neutral and charged channels are also measured. We obtain the following branching fractions and CP asymmetries: , , , and . The measured difference in CP asymmetries is , and the measured isospin asymmetry is ∆ 0+ = (+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.

A bstract We present a measurement of the ratio R μ = B τ − → μ − ν ¯ μ ν τ / B τ − → e − ν ¯ e ν τ of branching fractions B of the τ lepton decaying to muons or electrons using data collected with the Belle II detector at the SuperKEKB e + e − collider. The sample has an integrated luminosity of 362 ± 2 fb − 1 at a centre-of-mass energy of 10.58 GeV. Using an optimised event selection, a binned maximum likelihood fit is performed using the momentum spectra of the electron and muon candidates. The result, R μ = 0.9675 ± 0.0007 ± 0.0036, where the first uncertainty is statistical and the second is systematic, is the most precise to date. It provides a stringent test of the light-lepton universality, translating to a ratio of the couplings of the muon and electron to the W boson in τ decays of 0.9974 ± 0.0019, in agreement with the standard model expectation of unity.

A bstract We present the result of a search for the charged-lepton-flavor violating decay τ − → μ − μ + μ − using a 424 fb − 1 sample of data recorded by the Belle II experiment at the SuperKEKB e + e − collider. The selection of e + e − → τ + τ − events is based on an inclusive reconstruction of the non-signal tau decay, and on a boosted decision tree to suppress background. We observe one signal candidate, which is compatible with the expectation from background processes. We set a 90% confidence level upper limit of 1 . 9 × 10 − 8 on the branching fraction of the τ − → μ − μ + μ − decay, which is the most stringent bound 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 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.