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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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We report the results of the first search for decays to the final state using of data collected at the resonance with the Belle detector at the KEKB asymmetric-energy collider. The results are interpreted in terms of both direct baryon-number-violating decay and oscillations which follow the standard model decay . We observe no evidence for baryon number violation and set the 95% confidence-level upper limits on the ratio of baryon-number-violating and standard model branching fractions to be and on the effective angular frequency of mixing in oscillations to be (equivalent to ). Published by the American Physical Society2024more » « lessFree, publicly-accessible full text available August 1, 2025
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A<sc>bstract</sc> We perform the first search forCPviolation in$$ {D}_{(s)}^{+}\to {K}_S^0{K}^{-}{\pi}^{+}{\pi}^{+} $$ 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$$ {D}^{+}\to {K}_S^0{K}^{-}{\pi}^{+}{\pi}^{+} $$ decays, and better than 0.3% for$$ {D}_s^{+}\to {K}_S^0{K}^{-}{\pi}^{+}{\pi}^{+} $$ 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.more » « lessFree, publicly-accessible full text available April 1, 2026
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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 present a comprehensive study of decays using pairs collected with the Belle detector at the KEKB collider. This process is a suppressed charmless decay into two vector mesons and can exhibit interesting polarization and violation. The decay is observed for the first time with a significance of 7.9 standard deviations. We measure a branching fraction , a fraction of longitudinal polarization , and a time-integrated asymmetry , where the first uncertainties listed are statistical and the second are systematic. This is the first observation of and the first measurements of and for this decay. Published by the American Physical Society2024more » « lessFree, publicly-accessible full text available August 1, 2025
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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