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Using a data sample of $427.9{\mathrm{fb}}^{-1}$ collected by the Belle II detector at or near the $\mathrm{\Upsilon }\left(4S\right)$ and $\mathrm{\Upsilon }\left(10753\right)$ resonances, the cross sections for $e^{+}{e}^{-}\to h^{+}{h}^{-}J/\psi (h=\pi /K/p)$ at center-of-mass energies ranging from 3.8 GeV or the production threshold to $5.5/6.0/7.0\mathrm{GeV}$ have been measured via initial-state radiation. The cross sections for the processes $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ and $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\psi$ are consistent with previously published results. The cross sections for these channels obtained by combining with previous Belle results are also given. The process $e^{+}{e}^{-}\to p\overline{p}J/\psi$ is investigated for the first time. The yields are small and no significant structure is observed in the cross section versus energy. Searches for vector charmoniumlike states in the $h^{+}{h}^{-}J/\psi$ systems, and for associated intermediate states in the $h^{\pm }J/\psi$ systems, are also presented. 

We report the first search for the flavor-changing neutral-current decays $B\to X_s\nu \overline{\nu }$ , where $X_s$ is a hadronic system with strangeness equal to 1, in data collected with the Belle II detector at the SuperKEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The data sample corresponds to an integrated luminosity of $365{\mathrm{fb}}^{-1}$ collected at the $\mathrm{\Upsilon }\left(4S\right)$ resonance and $43{\mathrm{fb}}^{-1}$ collected at a center-of-mass energy 60 MeV below resonance for estimation of $e^{+}{e}^{-}\to q\overline{q}$ continuum background. One of the $B$ mesons from the $\mathrm{\Upsilon }\left(4S\right)\to B\overline{B}$ decay is fully reconstructed in a hadronic decay mode. The $B\to X_s\nu \overline{\nu }$ decay is reconstructed with a sum-of-exclusives approach that uses 30 $X_s$ decay modes. This approach provides high sensitivity to the inclusive decay, despite the presence of two undetected neutrinos. The search is performed in three regions of the $X_s$ mass, $M_{X_s}^{\mathrm{true}}$ , chosen to separate contributions from $K$ , $K^{*}\left(892\right)$ , and heavier strange final states. We do not observe a significant signal and set upper limits at 90% confidence level on the partial branching fractions for the regions $0.0<M_{X_s}^{\mathrm{true}}<0.6\mathrm{GeV}/c^2$ , $0.6<M_{X_s}^{\mathrm{true}}<1.0\mathrm{GeV}/c^2$ , and $1.0\mathrm{GeV}/c^2<M_{X_s}^{\mathrm{true}}$ of $2.2\times {10}^{-5}$ , $9.3\times {10}^{-5}$ , and $30.9\times {10}^{-5}$ , respectively. Combining the three mass regions, we obtain the upper limit on the branching fraction, $B(B\to X_s\nu \overline{\nu })<3.3\times {10}^{-4}$ . 

A<sc>bstract</sc> We study the processesχ_bJωandχ_bJ(π⁺π⁻π⁰)_non−ω(J= 0, 1, 2) at center-of-mass energies$$\sqrt{s}$$from 10.73 to 11.02 GeV using a 142.5 fb⁻¹data sample collected with the Belle detector at the KEKB asymmetric-energye⁺e⁻collider; and at$$\sqrt{s}\sim 10.75$$GeV using a 19.8 fb⁻¹sample collected with Belle II at SuperKEKB. We find that the Υ(10753) state decays intoχ_bJωbut not intoχ_bJ(π⁺π⁻π⁰)_non−ω, while the Υ(10860) state, in contrast, decays intoχ_bJ(π⁺π⁻π⁰)_non−ωbut not intoχ_bJω. The mass and width of the Υ(10753) state are measured to be (10756.1 ± 3.4(stat.) ± 2.7(syst.)) MeV/c²and (32.2 ± 11.3(stat.) ± 14.9(syst.)) MeV. The products of the partial width toe⁺e⁻and branching fractions for Υ(10753)→ χ_b1ωand Υ(10753)→ χ_b2ωare (1.57±0.27(stat.)±0.22(syst.)) eV and (1.39±0.41(stat.)±0.33(syst.)) eV. 

We measure the time- and phase-space-integrated $CP$ asymmetry ${\mathcal{A}}_{CP}$ in $D^0\to {\pi }^{+}{\pi }^{-}{\pi }^0$ decays reconstructed in $e^{+}{e}^{-}\to c\overline{c}$ events collected by the Belle II experiment from 2019 to 2022. This sample corresponds to an integrated luminosity of $428{\mathrm{fb}}^{-1}$ . We require $D^0$ mesons to be produced in $D^{*+}\to D^0{\pi }^{+}$ decays to determine their flavor at production. Control samples of $D^0\to K^{-}{\pi }^{+}$ decays are used to correct for reconstruction-induced asymmetries. The result, ${\mathcal{A}}_{CP}\left(D^0\to {\pi }^{+}{\pi }^{-}{\pi }^0\right)=(0.29\pm 0.27\pm 0.13)\%$ , where the first uncertainty is statistical and the second systematic, is the most precise result to date and is consistent with $CP$ conservation. 

A sample of $365{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}\to \mathrm{\Upsilon }\left(4S\right)\to B\overline{B}$ data collected by the Belle II experiment is used to measure the partial branching fractions of charmless semileptonic $B$ meson decays and determine the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $V_{ub}$ . Events containing a signal electron or muon $\ell$ and a fully reconstructed hadronic $B$ decay that constrains the signal kinematics are selected, while the rest of the event defines the hadronic system $X_u$ associated with the signal. To discriminate the signal from the 50-times larger background originating from CKM-favored semileptonic $B$ decays, a template fit is performed in both signal and control regions after applying an optimized selection. The partial branching fraction measured for lepton energies greater than 1 GeV in the signal $B$ meson rest frame is $\mathrm{\Delta }\mathcal{B}\left(B\to X_u\ell \nu \right)=(1.54\pm 0.08\left(\mathrm{stat}\right)\pm 0.12\left(\mathrm{syst}\right))\times {10}^{-3}$ . From this measurement, using the Gambino, Giordano, Ossola, Uraltsev theoretical framework, $\left|V_{ub}\right|=(4.01\pm 0.19_{-0.08}^{+0.07})\times {10}^{-3}$ is determined, where the uncertainties are experimental and theoretical, respectively. This value is consistent with the world average obtained from previous inclusive measurements. Different theoretical predictions and partial branching fractions measured in other phase-space regions, defined by additional selections on the $X_u$ and leptonic system masses, are also used to determine $\left|V_{ub}\right|$ . This allows for a comparison of the resulting values across theoretical frameworks and phase-space regions. 

A<sc>bstract</sc> We present a measurement of the time-dependentCPasymmetry in$${B}^{0}\to {K}_{\text{S}}^{0}{\pi }^{+}{\pi }^{-}\gamma $$decays using a data set of 365 fb⁻¹recorded by the Belle II experiment and the final data set of 711 fb⁻¹recorded by the Belle experiment at the Υ(4S) resonance. The direct and mixing-induced time-dependentCPviolation parametersCandSare determined along with two additional quantities,S⁺andS⁻, 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 areC=−0.17±0.09±0.04,S=−0.29±0.11±0.05,S⁺= −0.57±0.23±0.10 andS⁻= 0.31±0.24±0.05, where the first uncertainty is statistical and the second systematic. 

We present a comprehensive study of $B^0\to \omega \omega$ decays using $772\times {10}^{6}B\overline{B}$ pairs collected with the Belle detector at the KEKB $e^{+}{e}^{-}$ collider. This process is a suppressed charmless decay into two vector mesons and can exhibit interesting polarization and $CP$ violation. The decay is observed for the first time with a significance of 7.9 standard deviations. We measure a branching fraction $\mathcal{B}=(1.53\pm 0.29\pm 0.17)\times {10}^{-6}$ , a fraction of longitudinal polarization $f_L=0.87\pm 0.13\pm 0.13$ , and a time-integrated $CP$ asymmetry $A_{CP}=-0.44\pm 0.43\pm 0.11$ , where the first uncertainties listed are statistical and the second are systematic. This is the first observation of $B^0\to \omega \omega$ and the first measurements of $f_L$ and $A_{CP}$ for this decay. Published by the American Physical Society2024 

A<sc>bstract</sc> We report a search for an axion-like particleainB→K^(*)adecays using data collected with the Belle detector at the KEKB asymmetric-energy electron-positron collider. The search is based on a 711 fb⁻¹data sample collected at the Υ(4S) resonance energy, corresponding to a sample of 772 × 10⁶Υ(4S) 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 theKmodes and 0.16 GeV–4.20 GeV for theK^*modes. No significant signal is observed in any of the modes, and 90% confidence level upper limits are established on the coupling to theWboson,g_aW, as a function ofamass. The limits range from 3×10⁻⁶GeV⁻¹to 3×10⁻⁵GeV⁻¹, improving the current constraints ong_aWby a factor of two over the most stringent previous experimental results. 

A<sc>bstract</sc> We present the result of a search for the charged-lepton-flavor violating decaysτ⁻→ e^∓ℓ^±ℓ⁻, whereℓis a muon or an electron, using a data sample with an integrated luminosity of 428 fb⁻¹recorded by the Belle II experiment at the SuperKEKBe⁺e⁻collider. The selection ofe⁺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 × 10⁻⁸are set at the 90% confidence level. These results are the most stringent bounds to date for four of the modes. 

We present a measurement of the branching fraction and fraction of longitudinal polarization of $B^0\to {\rho }^{+}{\rho }^{-}$ decays, which have two ${\pi }^0$ ’s in the final state. We also measure time-dependent $CP$ violation parameters for decays into longitudinally polarized ${\rho }^{+}{\rho }^{-}$ pairs. This analysis is based on a data sample containing $(387\pm 6)\times {10}^6$ $\mathrm{\Upsilon }\left(4S\right)$ mesons collected with the Belle II detector at the SuperKEKB asymmetric-energy $e^{+}{e}^{-}$ collider in 2019–2022. We obtain $\mathcal{B}(B^0\to {\rho }^{+}{\rho }^{-})=\left(2.89_{-0.22}^{+0.23}{}_{-0.27}^{+0.29}\right)\times {10}^{-5}$ , $f_L=0.921_{-0.025}^{+0.024}{}_{-0.015}^{+0.017}$ , $S=-0.26\pm 0.19\pm 0.08$ , and $C=-0.02\pm 0.12_{-0.05}^{+0.06}$ , where the first uncertainties are statistical and the second are systematic. We use these results to perform an isospin analysis to constrain the Cabibbo-Kobayashi-Maskawa angle ${\varphi }_2$ and obtain two solutions; the result consistent with other Standard Model constraints is ${\varphi }_2=\left({92.6}_{-4.7}^{+4.5}\right)°$ . Published by the American Physical Society2025