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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> Using the data samples of 102 million Υ(1S) and 158 million Υ(2S) events collected by the Belle detector, we search for a pentaquark state in thepJ/ψfinal state from Υ(1,2S) inclusive decays. Here, the charge-conjugate$$\overline{p }J/\psi $$is included. We observe clearpJ/ψproduction in Υ(1,2S) decays and measure the branching fractions to be$$\mathcal{B}[\Upsilon (1S)\to pJ/\psi +anything]=[8.1\pm 0.6(stat.)\pm 0.5(syst.)]\times {10}^{-5}$$and$$\mathcal{B}[\Upsilon (2S)\to pJ/\psi +anything]=[4.3\pm 0.5(stat.)\pm 0.4(syst.)]\times {10}^{-5}$$. We also measure the cross section of inclusivepJ/ψproduction ine⁺e⁻annihilation to beσ(e⁺e⁻→pJ/ψ+anything) = [108 ± 11(stat.) ± 6(syst.)] fb at$$\sqrt{s}=10.52$$GeV using an 89.5 fb⁻¹continuum data sample. There is no significantP_c(4312)⁺,P_c(4440)⁺orP_c(4457)⁺signal found in thepJ/ψfinal states in Υ(1,2S) inclusive decays. We determine the upper limits of$$\mathcal{B}\left[\Upsilon \left({1},{2}S\right)\to {P}_{c}^{+}+anything\right]\cdot \mathcal{B}\left({P}_{c}^{+}\to pJ/\psi \right)$$to be at the 10⁻⁶level. 

We report the first evidence for the $h_b\left(2\mathrm{P}\right)\to \mathrm{\Upsilon }\left(1\mathrm{S}\right)\eta$transition with a significance of 3.5 standard deviations. The decay branching fraction is measured to be $\mathcal{B}\left[h_b\right(2\mathrm{P})\to \mathrm{\Upsilon }(1\mathrm{S}\left)\eta \right]=({7.1}_{-3.2}^{+3.7}\pm 0.8)\times {10}^{-3}$, which is noticeably smaller than expected. We also set upper limits on ${\pi }^0$transitions of $\mathcal{B}\left[h_b\right(2\mathrm{P})\to \mathrm{\Upsilon }(1\mathrm{S}\left){\pi }^0\right]<1.8\times {10}^{-3}$, and $\mathcal{B}\left[h_b\right(1\mathrm{P})\to \mathrm{\Upsilon }(1\mathrm{S}\left){\pi }^0\right]<1.8\times {10}^{-3}$, at the 90% confidence level. These results are obtained with a $131.4{\mathrm{fb}}^{-1}$data sample collected near the $\mathrm{\Upsilon }\left(5\mathrm{S}\right)$resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$collider. 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. 

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 perform an angular analysis of the $B\to K^{*}{e}^{+}{e}^{-}$decay for the dielectron mass squared, $q^2$, range of $0.0008–1.1200{\mathrm{GeV}}^2/c^4$using the full Belle dataset in the $K^{*0}\to K^{+}{\pi }^{-}$and $K^{*+}\to K_S^0{\pi }^{+}$channels, incorporating new methods of electron identification to improve the statistical power of the dataset. This analysis is sensitive to contributions from right-handed currents from physics beyond the Standard Model by constraining the Wilson coefficients ${\mathcal{C}}_7^{(\prime )}$. We perform a fit to the $B\to K^{*}{e}^{+}{e}^{-}$differential decay rate and measure the imaginary component of the transversality amplitude to be $A_T^{\mathrm{Im}}=-1.27\pm 0.52\pm 0.12$, and the $K^{*}$transverse asymmetry to be $A_T^{\left(2\right)}=0.52\pm 0.53\pm 0.11$, with $F_L$and $A_T^{\mathrm{Re}}$fixed to the Standard Model values. The resulting constraints on the value of ${\mathcal{C}}_7^{\prime }$are consistent with the Standard Model within a $2\sigma$confidence interval. Published by the American Physical Society2024