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We report a new measurement of transverse single-spin asymmetries for dijet production in collisions of polarized protons at $\sqrt{s}=200\mathrm{GeV}$. Correlations between the proton spin and the transverse momenta of its partons, each perpendicular to the proton momentum direction, are probed at high $Q^2\approx 160{\mathrm{GeV}}^2$. Evidence for nonzero Sivers effects is measured for the first time in dijets from proton-proton collisions, but only when the jets are sorted by their net charge, which enhances the otherwise canceling opposite-sign $u$- or $d$-quark contributions to separate data samples. The resulting asymmetries are compared to recent theoretical calculations. Separately, the associated Sivers observable $⟨k_T⟩$, the average parton transverse momentum, is extracted using a simple kinematics approach which further enables a determination of the individual partonic contributions to the observed asymmetries. 

We report the first observation of the radiative decay $D_{s0}^{*}(2317{)}^{+}\to D_s^{*+}\gamma$with a statistical significance exceeding 10 standard deviations. The signal is observed in the continuum $e^{+}{e}^{-}\to c\overline{c}$process, using combined data samples of $980.4{\mathrm{fb}}^{-1}$from Belle and $427.9{\mathrm{fb}}^{-1}$from Belle II, collected at the KEKB and SuperKEKB asymmetric-energy $e^{+}{e}^{-}$colliders, respectively. The branching fraction ratio $\mathcal{B}\left[D_{s0}^{*}\right(2317{)}^{+}\to D_s^{*+}\gamma ]/\mathcal{B}[D_{s0}^{*}(2317{)}^{+}\to D_s^{+}{\pi }^0]$is measured to be $[7.13\pm 0.70(\mathrm{stat})\pm 0.26(\mathrm{syst}\left)\right]\%$. This result provides crucial discrimination between theoretical models of the $D_{s0}^{*}(2317{)}^{+}$structure. 

We report measurements of production cross sections for ${\rho }^{+}$, ${\rho }^0$, $\omega$, $K^{*+}$, $K^{*0}$, $\varphi$, $\eta$, $K_S^0$, $f_0\left(980\right)$, $D^{+}$, $D^0$, $D_s^{+}$, $D^{*+}$, $D^{*0}$, and $D_s^{*+}$in $e^{+}{e}^{-}$collisions at a center-of-mass energy near 10.58 GeV. The data were recorded by the Belle experiment, consisting of $571{\mathrm{fb}}^{-1}$at 10.58 GeV and $74{\mathrm{fb}}^{-1}$at 10.52 GeV. Production cross sections are extracted as a function of the fractional hadron momentum $x_p$. The measurements are compared to Monte Carlo generator predictions with various fragmentation settings, including those that have increased fragmentation into vector mesons over pseudoscalar mesons. The cross sections measured for light hadrons are consistent with no additional increase of vector over pseudoscalar mesons. The charmed-meson cross sections are compared to earlier measurements—when available—including older Belle results, which they supersede. They are in agreement before application of an improved initial-state radiation correction procedure that causes slight changes in their $x_p$shapes. Published by the American Physical Society2025 

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 a measurement of the branching fraction for the leptonic decay $B^{+}\to {\mu }^{+}{\nu }_{\mu }$. This work presents the first $B^{+}\to {\mu }^{+}{\nu }_{\mu }$result using Belle II data, an updated Belle measurement that supersedes the previous result, and their combination, which yields the most precise search to date. The analysis is based on $1076{\mathrm{fb}}^{-1}$of $e^{+}{e}^{-}$collision data collected at a center-of-mass energy of 10.58 GeV with the Belle and Belle II detectors at the KEKB and SuperKEKB colliders, respectively. We measure $\mathcal{B}(B^{+}\to {\mu }^{+}{\nu }_{\mu })=(4.4\pm 1.9\pm 1.0)\times {10}^{-7}$, where the first uncertainty is statistical and the second systematic. The observed significance relative to the background-only hypothesis is 2.4 standard deviations. We set a 90% confidence level upper limit of $\mathcal{B}(B^{+}\to {\mu }^{+}{\nu }_{\mu })<6.7\times {10}^{-7}$using a frequentist approach and a 90% credibility level upper limit of $\mathcal{B}(B^{+}\to {\mu }^{+}{\nu }_{\mu })<7.2\times {10}^{-7}$using a Bayesian approach. These are the most stringent limits to date. The result is interpreted as an exclusion region in the parameter space of type II and type III two-Higgs-doublet models. We search for stable sterile neutrinos with masses $m_N\in [0,1.5]\mathrm{GeV}$. No signal is observed, and the resulting exclusion on the squared mixing parameter $|U_{\mu N}{|}^2$provides improvement over previous limits. We report a measurement of the partial branching fraction of semileptonic $B\to X_u\ell {\nu }_{\ell }$decays with $p_{\mu }^B>2.2\mathrm{GeV}$, obtaining $\mathrm{\Delta }\mathcal{B}(B\to X_u\ell {\nu }_{\ell })=(2.72\pm 0.05\pm 0.29)\times {10}^{-4}$. We present a model-dependent study of weak annihilation decays using the muon momentum spectrum. We observe a signal of 2.4 standard deviations above the background-only hypothesis in regions where the distribution resembles that of $B\to X_u\ell {\nu }_{\ell }$decays. 

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, $B(B\to X_s\nu \overline{\nu })<3.3\times {10}^{-4}$.