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We report measurements of production cross sections for , , , , , , , , , , , , , , and in collisions at a center-of-mass energy near 10.58 GeV. The data were recorded by the Belle experiment, consisting of at 10.58 GeV and at 10.52 GeV. Production cross sections are extracted as a function of the fractional hadron momentum . 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 shapes. Published by the American Physical Society2025more » « lessFree, publicly-accessible full text available March 1, 2026
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In the bottomonium sector, the hindered magnetic dipole transitions between P-wave states , , 1, 2, are expected to be severely suppressed according to the relativized quark model, due to the spin flip of the quark. Nevertheless, a recent model following the coupled-channel approach predicts the corresponding branching fractions to be enhanced by orders of magnitude. In this Letter, we report the first search for such transitions. We find no significant signals and set upper limits at 90% confidence level on the corresponding branching fractions: , and . These values help to constrain the parameters of the coupled-channel models. The results are obtained using a data sample taken around with the Belle detector at the KEKB asymmetric-energy collider. Published by the American Physical Society2025more » « lessFree, publicly-accessible full text available January 1, 2026
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We report the first evidence for the transition with a significance of 3.5 standard deviations. The decay branching fraction is measured to be , which is noticeably smaller than expected. We also set upper limits on transitions of , and , at the 90% confidence level. These results are obtained with a data sample collected near the resonance with the Belle detector at the KEKB asymmetric-energy collider. Published by the American Physical Society2024more » « lessFree, publicly-accessible full text available December 1, 2025
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We present a measurement of the branching fraction and fraction of longitudinal polarization of decays, which have two ’s in the final state. We also measure time-dependent violation parameters for decays into longitudinally polarized pairs. This analysis is based on a data sample containing mesons collected with the Belle II detector at the SuperKEKB asymmetric-energy collider in 2019–2022. We obtain , , , and , 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 and obtain two solutions; the result consistent with other Standard Model constraints is . Published by the American Physical Society2025more » « lessFree, publicly-accessible full text available May 1, 2026
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We report the results of the first search for Standard Model and baryon-number-violating two-body decays of the neutral mesons to and using of data collected at the resonance with the Belle detector at the KEKB asymmetric-energy collider. We observe no evidence of signal from any such decays and set 95% confidence-level upper limits on the products of and branching fractions for these two-body decays with in the range between and . Published by the American Physical Society2024more » « lessFree, publicly-accessible full text available August 1, 2025
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We measure the complete set of angular coefficients for exclusive decays ( , ). Our analysis uses the full Belle dataset with hadronic tag-side reconstruction. The results allow us to extract the form factors describing the transition and the Cabibbo-Kobayashi-Maskawa matrix element . Using recent lattice QCD calculations for the hadronic form factors, we find using the Boyd-Grinstein-Lebed parametrization, compatible with determinations from inclusive semileptonic decays. We search for lepton flavor universality violation as a function of the hadronic recoil parameter and investigate the differences of the electron and muon angular distributions. We find no deviation from standard model expectations. Published by the American Physical Society2024more » « lessFree, publicly-accessible full text available September 1, 2025
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A<sc>bstract</sc> Using data samples of 983.0 fb−1and 427.9 fb−1accumulated with the Belle and Belle II detectors operating at the KEKB and SuperKEKB asymmetric-energye+e−colliders, singly Cabibbo-suppressed decays$$ {\Xi}_c^{+}\to p{K}_S^0 $$ ,$$ {\Xi}_c^{+}\to \Lambda {\pi}^{+} $$ , and$$ {\Xi}_c^{+}\to {\Sigma}^0{\pi}^{+} $$ are observed for the first time. The ratios of branching fractions of$$ {\Xi}_c^{+}\to p{K}_S^0 $$ ,$$ {\Xi}_c^{+}\to \Lambda {\pi}^{+} $$ , and$$ {\Xi}_c^{+}\to {\Sigma}^0{\pi}^{+} $$ relative to that of$$ {\Xi}_c^{+}\to {\Xi}^{-}{\pi}^{+}{\pi}^{+} $$ are measured to be$$ {\displaystyle \begin{array}{c}\frac{\mathcal{B}\left({\Xi}_c^{+}\to p{K}_S^0\right)}{\mathcal{B}\left({\Xi}_c^{+}\to {\Xi}^{-}{\pi}^{+}{\pi}^{+}\right)}=\left(2.47\pm 0.16\pm 0.07\right)\%,\\ {}\frac{\mathcal{B}\left({\Xi}_c^{+}\to \Lambda {\pi}^{+}\right)}{\mathcal{B}\left({\Xi}_c^{+}\to {\Xi}^{-}{\pi}^{+}{\pi}^{+}\right)}=\left(1.56\pm 0.14\pm 0.09\right)\%,\\ {}\frac{\mathcal{B}\left({\Xi}_c^{+}\to {\Sigma}^0{\pi}^{+}\right)}{\mathcal{B}\left({\Xi}_c^{+}\to {\Xi}^{-}{\pi}^{+}{\pi}^{+}\right)}=\left(4.13\pm 0.26\pm 0.22\right)\%.\end{array}} $$ Multiplying these values by the branching fraction of the normalization channel,$$ \mathcal{B}\left({\Xi}_c^{+}\to {\Xi}^{-}{\pi}^{+}{\pi}^{+}\right)=\left(2.9\pm 1.3\right)\% $$ , the absolute branching fractions are determined to be$$ {\displaystyle \begin{array}{c}\mathcal{B}\left({\Xi}_c^{+}\to p{K}_S^0\right)=\left(7.16\pm 0.46\pm 0.20\pm 3.21\right)\times {10}^{-4},\\ {}\mathcal{B}\left({\Xi}_c^{+}\to \Lambda {\pi}^{+}\right)=\left(4.52\pm 0.41\pm 0.26\pm 2.03\right)\times {10}^{-4},\\ {}\mathcal{B}\left({\Xi}_c^{+}\to {\Sigma}^0{\pi}^{+}\right)=\left(1.20\pm 0.08\pm 0.07\pm 0.54\right)\times {10}^{-3}.\end{array}} $$ The first and second uncertainties above are statistical and systematic, respectively, while the third ones arise from the uncertainty in$$ \mathcal{B}\left({\Xi}_c^{+}\to {\Xi}^{-}{\pi}^{+}{\pi}^{+}\right) $$ .more » « lessFree, publicly-accessible full text available March 1, 2026
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We measure the branching fraction and -violating flavor-dependent rate asymmetry of decays reconstructed using the Belle II detector in an electron-positron collision sample containing mesons. Using an optimized event selection, we find signal decays in a fit to background-discriminating and flavor-sensitive distributions. The resulting branching fraction is and the -violating asymmetry is . Published by the American Physical Society2025more » « lessFree, publicly-accessible full text available April 1, 2026
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A<sc>bstract</sc> We report measurements of the absolute branching fractions$$\mathcal{B}\left({B}_{s}^{0}\to {D}_{s}^{\pm }X\right)$$,$$\mathcal{B}\left({B}_{s}^{0}\to {D}^{0}/{\overline{D} }^{0}X\right)$$, and$$\mathcal{B}\left({B}_{s}^{0}\to {D}^{\pm }X\right)$$, where the latter is measured for the first time. The results are based on a 121.4 fb−1data sample collected at the Υ(10860) resonance by the Belle detector at the KEKB asymmetric-energye+e−collider. We reconstruct one$${B}_{s}^{0}$$meson in$${e}^{+}{e}^{-}\to \Upsilon\left(10860\right)\to {B}_{s}^{*}{\overline{B} }_{s}^{*}$$events and measure yields of$${D}_{s}^{+}$$,D0, andD+mesons in the rest of the event. We obtain$$\mathcal{B}\left({B}_{s}^{0}\to {D}_{s}^{\pm }X\right)=\left(68.6\pm 7.2\pm 4.0\right)\%$$,$$\mathcal{B}\left({B}_{s}^{0}\to {D}^{0}/{\overline{D} }^{0}X\right)=\left(21.5\pm 6.1\pm 1.8\right)\%$$, and$$\mathcal{B}\left({B}_{s}^{0}\to {D}^{\pm }X\right)=\left(12.6\pm 4.6\pm 1.3\right)\%$$, where the first uncertainty is statistical and the second is systematic. Averaging with previous Belle measurements gives$$\mathcal{B}\left({B}_{s}^{0}\to {D}_{s}^{\pm }X\right)=\left(63.4\pm 4.5\pm 2.2\right)\%$$and$$\mathcal{B}\left({B}_{s}^{0}\to {D}^{0}/{\overline{D} }^{0}X\right)=\left(23.9\pm 4.1\pm 1.8\right)\%$$. For the$${B}_{s}^{0}$$production fraction at the Υ(10860), we find$${f}_{s}=\left({21.4}_{-1.7}^{+1.5}\right)\%$$.more » « lessFree, publicly-accessible full text available April 1, 2026
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We report a search for a heavy neutral lepton (HNL) that mixes predominantly with . The search utilizes data collected with the Belle detector at the KEKB asymmetric energy collider. The data sample was collected at and just below the center-of-mass energies of the and resonances and has an integrated luminosity of , corresponding to events. We search for production of the HNL (denoted ) in the decay followed by its decay via . The search focuses on the parameter-space region in which the HNL is long-lived, so that the originate from a common vertex that is significantly displaced from the collision point of the KEKB beams. Consistent with the expected background yield, one event is observed in the data sample after application of all the event-selection criteria. We report limits on the mixing parameter of the HNL with the neutrino as a function of the HNL mass. Published by the American Physical Society2024more » « less