The experimental results on the ratios of branching fractions R(D)=B(Bover ¯→Dτ^{-}νover ¯_{τ})/B(Bover ¯→Dℓ^{-}νover ¯_{ℓ}) and R(D^{*})=B(Bover ¯→D^{*}τ^{-}νover ¯_{τ})/B(Bover ¯→D^{*}ℓ^{-}νover ...¯_{ℓ}), where ℓ denotes an electron or a muon, show a long-standing discrepancy with the standard model predictions, and might hint at a violation of lepton flavor universality. We report a new simultaneous measurement of R(D) and R(D^{*}), based on a data sample containing 772×10^{6} BBover ¯ events recorded at the ϒ(4S) resonance with the Belle detector at the KEKB e^{+}e^{-} collider. In this analysis the tag-side B meson is reconstructed in a semileptonic decay mode and the signal-side τ is reconstructed in a purely leptonic decay. The measured values are R(D)=0.307±0.037±0.016 and R(D^{*})=0.283±0.018±0.014, where the first uncertainties are statistical and the second are systematic. These results are in agreement with the standard model predictions within 0.2, 1.1, and 0.8 standard deviations for R(D), R(D^{*}), and their combination, respectively. This work constitutes the most precise measurements of R(D) and R(D^{*}) performed to date as well as the first result for R(D) based on a semileptonic tagging method.
Here, we present a measurement of angular observables and a test of lepton flavor universality in the B → K*ℓ+ℓ- decay, where ℓ is either e or μ . The analysis is performed on a data sample ...corresponding to an integrated luminosity of 711fb-1 containing 772×106 B B ¯ pairs, collected at the Υ ( 4S ) resonance with the Belle detector at the asymmetric-energy e+e- collider KEKB. The finding is consistent with standard model (SM) expectations, where the largest discrepancy from a SM prediction is observed in the muon modes with a local significance of 2.6σ .
We report the result for a search for the leptonic decay of B+→μ+νμ using the full Belle dataset of 711 fb−1 of integrated luminosity at the ϒ(4S) resonance. In the Standard Model leptonic B-meson ...decays are helicity and Cabibbo-Kobayashi-Maskawa suppressed. To maximize sensitivity an inclusive tagging approach is used to reconstruct the second B meson produced in the collision. The directional information from this second B meson is used to boost the observed μ into the signal B-meson rest frame, in which the μ has a monochromatic momentum spectrum. Though its momentum is smeared by the experimental resolution, this technique improves the analysis sensitivity considerably. Analyzing the μ momentum spectrum in this frame we find B(B+→μ+νμ)=(5.3±2.0±0.9)×10−7 with a one-sided significance of 2.8 standard deviations over the background-only hypothesis. This translates to a frequentist upper limit of B(B+→μ+νμ)<8.6×10−7 at 90% confidence level. The experimental spectrum is then used to search for a massive sterile neutrino, B+→μ+N, but no evidence is observed for a sterile neutrino with a mass in a range of 0–1.5 GeV. The determined B+→μ+νμ branching fraction limit is further used to constrain the mass and coupling space of the type II and type III two-Higgs-doublet models.
We report a study of the charmless hadronic decay of the charged B meson to the three-body final state K+K−π+. The results are based on a data sample that contains 772×106 BB¯ pairs collected at the ...ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. The measured inclusive branching fraction and direct CP asymmetry are (5.38±0.40±0.35)×10−6 and −0.170±0.073±0.017, respectively, where the first uncertainties are statistical and the second are systematic. The K+K− invariant mass distribution of the signal candidates shows an excess in the region below 1.5 GeV/c2, which is consistent with the previous studies from BABAR and LHCb. In addition, strong evidence of a large direct CP asymmetry is found in the low K+K− invariant-mass region.
We report a search for X(3872) and X(3915) in B+→χc1π0K+ decays. We set an upper limit of B(B+→X(3872)K+)×B(X(3872)→χc1π0)<8.1×10−6 and B(B+→X(3915)K+)×B(X(3915)→χc1π0)<3.8×10−5 at 90% confidence ...level. We also measure B(X(3872)→χc1π0)/B(X(3872)→J/ψπ+π−)<0.97 at 90% confidence level. The results reported here are obtained from 772×106 BB events collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider.
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 new measurement of the exclusive e+e−→D(*)±D*∓ cross sections as a function of the center-of-mass energy from the D(*)±D*∓ threshold through s=6.0 GeV, using the initial-state radiation ...technique. The analysis is based on a data sample collected with the Belle detector with an integrated luminosity of 951 fb−1. The accuracy of the cross section measurement is increased by a factor of 2 over the first Belle study. We perform the first angular analysis of the e+e−→D*±D*∓ process and decompose this exclusive cross section into three components corresponding to the D* helicities.
We report the first measurement of the charm-mixing parameter yCP in D0 decays to the CP-odd final state ... The study uses the full Belle e+e− annihilation data sample of 976 fb−1 taken at or near ...the ϒð4SÞ centre-of-mass energy. We find ..., where the first uncertainty is statistical, the second is systematic due to event selection and background, and the last is due to possible presence of CP-even decays in the data sample. (ProQuest: ... denotes formula omitted.)
The first dedicated search for the ηc2(1D) is carried out using the decays B+ → ηc2(1D)K+, B0 → ηc2(1D)K$0\atop{S}$, B0 → ηc2(1D)π-K+, and B+ → ηc2(1D)π +K$0\atop{S}$ with ηc2(1D) → hcγ. No ...significant signal is found. For the ηc2(1D) mass range between 3795 and 3845 MeV/c2, the branching-fraction upper limits are determined to be B(B+ → ηc2(1D)K+) × B(ηc2(1D) → hcγ) < 3.7 × 10-5 , B(B0 → ηc2(1D)K$0\atop{S}$) × B(ηc2(1D) → hcγ) < 3.5 × 10-5, B(B0 → ηc2(1D)π-K+) × B(ηc2(1D) → hcγ) < 1.0 × 10-4, and B(B+ → ηc2(1D)π+K$0\atop{S}$) × B(ηc2(1D) → hcγ) < 1.1 × 10-4 at 90% C. L. The analysis is based on the 711 fb-1 data sample collected on the Υ(4S) resonance by the Belle detector, which operated at the KEKB asymmetric-energy e+e- collider.
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