Using data collected in the Belle experiment at the KEKB asymmetric-energy e+e - collider we search for transitions ?(4S) ? ?b(1S)?, ?(5S) ? ?b(1S)? and ?(5S) ? ?b(2S)?. No significant signals are ...observed and we set 90% confidence level upper limits on the corresponding visible cross sections: 0.2 pb, 0.4 pb and 1.9 pb, respectively
Here, we search for CP violation in the singly-Cabibbo-suppressed decay D0 → K+K–π+π– using data corresponding to an integrated luminosity of 988 fb–1 collected by the Belle detector at the KEKB e+e– ...collider. We measure a set of five kinematically dependent CP asymmetries, of which four asymmetries are measured for the first time. The set of asymmetry measurements can be sensitive to CP violation via interference between the different partial-wave contributions to the decay and performed on other pseudoscalar decays. We find no evidence of CP violation.
We present the first measurements of branching fractions of rare tau-lepton decays, τ− →π−ντℓ+ℓ− (ℓ = e or μ), using a data sample corresponding to 562 fb−1 collected at a center-of-mass energy of ...10.58 GeV with the Belle detector at the KEKB asymmetric-energy e+e− collider. The τ−→π−ντe+e− decay is observed for the first time with 7.0σ significance. The partial branching fraction determined by the structure-dependent mechanisms mediated by either a vector or an axial-vector current for the mass region Mπee > 1.05 GeV/c2 is measured to be B(τ− →π−ντe+e−)Mπ−e+e− > 1.05 GeV/c2 = (5.90 ± 0.53 ± 0.85 ± 0.11) × 10−6, where the first uncertainty is statistical, the second is systematic, and the third is due to model dependence. In the full phase space, due to the different detection efficiencies for the structure-dependent mechanisms mediated by axial-vector and vector currents, the branching fraction varies from BA(τ−→π−ντe+e−) = (1.46 ± 0.13 ± 0.21) × 10−5 to BV(τ−→π−ντe+e−) = (3.01 ± 0.27 ± 0.43) × 10−5, respectively. An upper limit is set on the branching fraction of the τ−→π−ντμ+μ− decay, B(τ− →π−ντμ+μ−) < 1.14 × 10−5, at the 90% confidence level.
We report a study of Λc+→Λh+ and Λc+→Σ0h+ (h=K,π) decays based on a data sample of 980fb-1 collected with the Belle detector at the KEKB energy-asymmetric e+e- collider. The first results of direct ...CP asymmetry in two-body singly Cabibbo-suppressed (SCS) decays of charmed baryons are measured, ACPdir(Λc+→ΛK+)=+0.021±0.026±0.001 and ACPdir(Λc+→Σ0K+)=+0.025±0.054±0.004. We also make the most precise measurement of the decay asymmetry parameters (α) for the four modes of interest and search for CP violation via the α-induced CP asymmetry (ACPα). We measure ACPα(Λc+→ΛK+)=-0.023±0.086±0.071 and ACPα(Λc+→Σ0K+)=+0.08±0.35±0.14, which are the first ACPα results for SCS decays of charmed baryons. We search for Λ-hyperon CP violation in Λc+→(Λ,Σ0)π+ and find ACPα(Λ→pπ-)=+0.013±0.007±0.011. This is the first time that hyperon CP violation has been measured via Cabibbo-favored charm decays. No evidence of baryon CP violation is found. We also obtain the most precise branching fractions for two SCS Λc+ decays, B(Λc+→ΛK+)=(6.57±0.17±0.11±0.35)×10-4 and B(Λc+→Σ0K+)=(3.58±0.19±0.06±0.19)×10-4. The first uncertainties are statistical and the second systematic, while the third uncertainties come from the uncertainties on the world average branching fractions of Λc+→(Λ,Σ0)π+.
We have searched for the lepton-flavor-violating decay B0→K*0μ±e∓ using a data sample of 711 fb−1 that contains 772×106 BB¯ pairs. The data were collected near the ϒ(4S) resonance with the Belle ...detector at the KEKB asymmetric-energy e+e− collider. No signals were observed, and we set 90% confidence level upper limits on the branching fractions of B(B0→K*0μ+e−)<1.2×10−7, B(B0→K*0μ−e+)<1.6×10−7, and, for both decays combined, B(B0→K*0μ±e∓)<1.8×10−7. These are the most stringent limits on these decays to date.
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