We report the results of the first search for the decay B0s → η′η using 121.4 fb−1 of data collected at the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We ...observe no significant signal and set a 90% confidence-level upper limit of 6.5 × 10−5 on the branching fraction of this decay.
We study the decay B+→K+K– π+ and investigate the angular distribution of K+K– pairs with invariant mass below 1.1 GeV / c2. This region exhibits both a strong enhancement in signal and very large ...direct CP violation. We construct a coherent sum model for the angular distribution of the S- and P-wave, and report the ratio of their amplitudes, the relative phase and the forward-backward asymmetry. We also report absolute differential branching fractions and direct CP asymmetry for the decay in bins of MK+K– and the differential branching fractions in bins of MK+π–. The results are based on a data sample that contains 772 × 106 $B\bar{B}$ pairs collected at the $Υ$(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e– collider. The result favors the presence of S- and D-waves in low MK+K– region to the detriment of a P-wave.
Using data collected in the Belle experiment at the KEKB asymmetric-energy e+ e− collider we search for transitions Υ ( 4S ) → ηb ( 1S )ω, Υ ( 5S ) → ηb ( 1S )ω and Υ ( 5S ) → ηb ( 2S ) ω. 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.
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.
We present a measurement of R_{K^{*}}, the branching fraction ratio B(B→K^{*}μ^{+}μ^{-})/B(B→K^{*}e^{+}e^{-}), for both charged and neutral B mesons. The ratio for the charged case R_{K^{*+}} is the ...first measurement ever performed. In addition, we report absolute branching fractions for the individual modes in bins of the squared dilepton invariant mass q^{2}. The analysis is based on a data sample of 711 fb^{-1}, containing 772×10^{6} BBover ¯ events, recorded at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The obtained results are consistent with standard model expectations.
With the full data sample of 772×106 BB¯ pairs recorded by the Belle detector at the KEKB electron-positron collider, the decay B¯→D*τ−ν¯τ is studied with the hadronic τ decays τ−→π−ντ and τ−→ρ−ντ. ...The τ polarization Pτ(D*) in two-body hadronic τ decays is measured, as well as the ratio of the branching fractions R(D*)=B(B¯→D*τ−ν¯τ)/B(B¯→D*ℓ−ν¯ℓ), where ℓ− denotes an electron or a muon. Our results, Pτ(D*)=−0.38±0.51(stat)−0.16+0.21(syst) and R(D*)=0.270±0.035(stat)−0.025+0.028(syst), are consistent with the theoretical predictions of the standard model. The polarization values of Pτ(D*)>+0.5 are excluded at the 90% confidence level.
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 711 fb^{-1} containing 772×10^{6} BBover ¯ pairs, collected at the ϒ(4S) resonance with the Belle detector at the asymmetric-energy e^{+}e^{-} collider KEKB. The result 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 present a new measurement of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb| from B0→D*−ℓ+νℓ decays, reconstructed with the full Belle data set of 711 fb−1 integrated luminosity. Two form ...factor parametrizations, originally conceived by the Caprini-Lellouch-Neubert (CLN) and the Boyd, Grinstein and Lebed (BGL) groups, are used to extract the product F(1)ηEW|Vcb| and the decay form factors, where F(1) is the normalization factor and ηEW is a small electroweak correction. In the CLN parametrization we find F(1)ηEW|Vcb|=(35.06±0.15±0.56)×10−3, ρ2=1.106±0.031±0.007, R1(1)=1.229±0.028±0.009, R2(1)=0.852±0.021±0.006. For the BGL parametrization we obtain F(1)ηEW|Vcb|=(34.93±0.23±0.59)×10−3, which is consistent with the world average when correcting for F(1)ηEW. The branching fraction of B0→D*−ℓ+νℓ is measured to be B(B0→D*−ℓ+νℓ)=(4.90±0.02±0.16)%. We also present a new test of lepton flavor universality violation in semileptonic B decays, B(B0→D*−e+ν)B(B0→D*−μ+ν)=1.01±0.01±0.03. The errors quoted correspond to the statistical and systematic uncertainties, respectively. This is the most precise measurement of F(1)ηEW|Vcb| and form factors to date and the first experimental study of the BGL form factor parametrization in an experimental measurement.
We search for CP violation in neutral charm meson decays using a data sample with an integrated luminosity of 9666 fb super(-1) collected with the Belle detector at the KEKB e super(+)e super(-) ...asymmetric-energy collider. The asymmetry obtained in the rate of D super(0) and D super(0) decays to the pi super(0)pi super(0) final state, -0.03 + or - 0.64(stat) + or - 0.10(syst)%, is consistent with no CP violation. This constitutes an order of magnitude improvement over the existing result. We also present an updated measurement of the CP asymmetry in D super(0) arrow right K super(0) sub(S) pi super(0) the decay: A sub(CP)(D super(0) arrow right K super(0) sub(S) pi super(0)) = -0.21 + or - 0.16(stat) + or - 0.07(syst)%.
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