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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 search for the $e^{+}{e}^{-}\to \gamma {\chi }_{bJ}$ ( $J=0$ , 1, 2) processes at center-of-mass energies $\sqrt{s}=10.653$ , 10.701, 10.746, and 10.804 GeV. These data were collected with the Belle II detector at the SuperKEKB collider and correspond to 3.5, 1.6, 9.8, and $4.7{\mathrm{fb}}^{-1}$ of integrated luminosity, respectively. We set upper limits at the 90% confidence level on the Born cross sections for $e^{+}{e}^{-}\to \gamma {\chi }_{bJ}$ at each center-of-mass energy $\sqrt{s}$ near 10.746 GeV. The upper limits at 90% confidence level on the Born cross sections for $e^{+}{e}^{-}\to \gamma {\chi }_{b1}$ are significantly smaller than the corresponding measured values for $e^{+}{e}^{-}\to \omega {\chi }_{b1}$ and $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}\mathrm{\Upsilon }\left(2S\right)$ at $\sqrt{s}=10.746\mathrm{GeV}$ . 

We present an analysis of the processes $e^{+}{e}^{-}\to \eta \mathrm{\Upsilon }\left(1S\right)$ , $\eta \mathrm{\Upsilon }\left(2S\right)$ , and $\gamma X_b$ with $X_b\to {\pi }^{+}{\pi }^{-}{\chi }_{bJ},{\chi }_{bJ}\to \gamma \mathrm{\Upsilon }\left(1S\right)$ ( $J=1$ , 2) reconstructed from $\gamma \gamma {\pi }^{+}{\pi }^{-}{\ell }^{+}{\ell }^{-}$ $(\ell =e,\mu )$ final states in $19.6{\mathrm{fb}}^{-1}$ of Belle II data collected at four energy points near the peak of the $\mathrm{\Upsilon }\left(10753\right)$ resonance. Here, $X_b$ is a hypothetical bottomonium-sector partner of the $X\left(3872\right)$ . In the process $e^{+}{e}^{-}\to \eta \mathrm{\Upsilon }\left(2S\right)$ , we observe a signal with a significance that exceeds $6.0\sigma$ when all energy points are combined. A signal with a significance of $4.2\sigma$ is observed at a center-of-mass energy of 10.653 GeV, close to the $B^{*}{\overline{B}}^{*}$ threshold. At this energy, we measure $\sigma \left(\eta \mathrm{\Upsilon }\right(2S\left)\right)/\sigma \left({\pi }^{+}{\pi }^{-}\mathrm{\Upsilon }\right(2S\left)\right)>23$ at the 90% confidence level, indicating a strong violation of heavy-quark spin symmetry. No significant signal is observed for $e^{+}{e}^{-}\to \eta \mathrm{\Upsilon }\left(1S\right)$ or $\gamma X_b$ . Upper limits on the Born cross sections for the processes $e^{+}{e}^{-}\to \eta \mathrm{\Upsilon }\left(1S\right)$ and $e^{+}{e}^{-}\to \gamma X_b$ with $X_b\to {\pi }^{+}{\pi }^{-}{\chi }_{bJ}$ are determined. 

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. 

We present a determination of the Cabibbo-Kobayashi-Maskawa matrix element $\left|V_{cb}\right|$ from the decay $B\to D\ell {\nu }_{\ell }$ using a $365{\mathrm{fb}}^{-1}$ $e^{+}{e}^{-}\to \mathrm{\Upsilon }\left(4S\right)\to B\overline{B}$ data sample recorded by the Belle II experiment at the SuperKEKB collider. The semileptonic decay of one $B$ meson is reconstructed in the modes $B^0\to D^{-}(\to K^{+}{\pi }^{-}{\pi }^{-}){\ell }^{+}{\nu }_{\ell }$ and $B^{+}\to {\overline{D}}^0(\to K^{+}{\pi }^{-}){\ell }^{+}{\nu }_{\ell }$ , where $\ell$ denotes either an electron or a muon. Charge conjugation is implied. The second $B$ meson in the $\mathrm{\Upsilon }\left(4S\right)$ event is not reconstructed explicitly. Using an inclusive reconstruction of the unobserved neutrino momentum, we determine the recoil variable $w=v_B·v_D$ , where $v_B$ and $v_D$ are the four-velocities of the $B$ and $D$ mesons. We measure the total decay branching fractions to be $\mathcal{B}(B^0\to D^{-}{\ell }^{+}{\nu }_{\ell })=(2.06\pm 0.05(\mathrm{stat})\pm 0.10(\mathrm{sys}\left)\right)\%$ and $\mathcal{B}(B^{+}\to {\overline{D}}^0{\ell }^{+}{\nu }_{\ell })=(2.31\pm 0.04(\mathrm{stat})\pm 0.09(\mathrm{sys}\left)\right)\%$ . We probe lepton flavor universality by measuring $\mathcal{B}(B\to De{\nu }_e)/\mathcal{B}(B\to D\mu {\nu }_{\mu })=1.020\pm 0.020\left(\mathrm{stat}\right)\pm 0.022\left(\mathrm{sys}\right)$ . Fitting the partial decay branching fraction as a function of $w$ and using the average of lattice QCD calculations of the $B\to D$ form factor, we obtain $\left|V_{cb}\right|=(39.2\pm 0.4(\mathrm{stat})\pm 0.6(\mathrm{sys})\pm 0.5(\mathrm{th}\left)\right)\times {10}^{-3}$ . 

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 

A<sc>bstract</sc> We perform the first search forCPviolation in$$ {D}_{(s)}^{+}\to {K}_S^0{K}^{-}{\pi}^{+}{\pi}^{+} $$ $D_{\left(s\right)}^{+}\to K_S^0{K}^{-}{\pi }^{+}{\pi }^{+}$ decays. We use a combined data set from the Belle and Belle II experiments, which studye⁺e⁻collisions at center-of-mass energies at or near the Υ(4S) resonance. We use 980 fb⁻¹of data from Belle and 428 fb⁻¹of data from Belle II. We measure sixCP-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$$ {D}^{+}\to {K}_S^0{K}^{-}{\pi}^{+}{\pi}^{+} $$ $D^{+}\to K_S^0{K}^{-}{\pi }^{+}{\pi }^{+}$ decays, and better than 0.3% for$$ {D}_s^{+}\to {K}_S^0{K}^{-}{\pi}^{+}{\pi}^{+} $$ $D_s^{+}\to K_S^0{K}^{-}{\pi }^{+}{\pi }^{+}$ decays. No evidence ofCPviolation is found. Our results for the triple-product asymmetries are the most precise to date for singly-Cabibbo-suppressedD⁺decays. Our results for the other asymmetries are the first such measurements performed for charm decays.