We present a search for lepton-flavor-violating τ decays into three leptons (electrons or muons) using 782 fb−1 of data collected with the Belle detector at the KEKB asymmetric-energy e+e− collider. ...No evidence for these decays is observed and we set 90% confidence level upper limits on the branching fractions between 1.5×10−8 and 2.7×10−8.
We search for lepton-flavor and lepton-number-violating τ decays into a lepton (ℓ= electron or muon) and two charged mesons (h,h′=π± or K±) using 854 fb−1 of data collected with the Belle detector at ...the KEKB asymmetric-energy e+e− collider. We obtain 90% confidence level upper limits on the τ→ℓhh′ branching fractions in the range (2.0–8.4)×10−8. These results improve upon our previously published upper limits by factors of about 1.8 on average.
We have studied hadronic τ decay modes involving an η meson using 490 fb−1 of data collected with the Belle detector at the KEKB asymmetric-energy e+e− collider. The following branching fractions ...have been measured: B(τ−→K−ηντ)=(1.58±0.05±0.09)×10−4, B(τ−→K−π0ηντ)=(4.6±1.1±0.4)×10−5, B(τ−→π−π0ηντ)=(1.35±0.03±0.07)×10−3, B(τ−→π−KS0ηντ)=(4.4±0.7±0.2)×10−5, and B(τ−→K∗−ηντ)=(1.34±0.12±0.09)×10−4. These results are substantially more precise than previous measurements. The new measurements are compared with theoretical calculations based on the CVC hypothesis or the chiral perturbation theory. We also set upper limits on branching fractions for τ decays into K−KS0ηντ, π−KS0π0ηντ, K−ηηντ, π−ηηντ and non-resonant K−π0ηντ final states.
We report first observations of Bs0→J/ψη and Bs0→J/ψη'. The results are obtained from 121.4 fb⁻¹ of data collected at the Υ(5S) resonance with the Belle detector at the KEKB e⁺e⁻ collider. We obtain ...the branching fractions B(Bs0→J/ψη)=5.10±0.50(stat)±0.25(syst)+1.14-0.79(NB(*)sB¯¯¯(*)s)×10⁻⁴, and B(Bs0→J/ψη')=3.71±0.61(stat)±0.18(syst)+0.83-0.57(NB(*)sB¯¯¯(*)s)×10⁻⁴. The ratio of the two branching fractions is measured to be (B(Bs→J/ψη'))/(B(Bs→J/ψη))=0.73±0.14(stat)±0.02(syst).
Using a sample of 158 x 10 super(6) Upsilon(2S) events collected with the Belle detector, we search for the first time for double-charmonium decays of the P-wave spin-triplet bottomonium states ...(Upsilon(2S) arrow right gamma chi bJ, arrow right J/psiJ/psipsi',psi 'psi' for J = 0, 1, and 2). No significant chi bJ signal is observed in the double-charmonium mass spectra, and we obtain the following upper limits: Bernoulli( chi bJ arrow right J/psiJ/psi) < 7.1 x 10 super(-5) 2.7 x 10 super(-5), 4.5 x 10 super(-5), Bernoulli( chi bJ arrow right J/psipsi) < 1.2 x 10 super(-4), 1.7 x 10 super(-5), 4.9 x 10 super(-5), Bernoulli( chi bJ arrow right psi'psi') < 3.1 x 10 super(-5), 6.2 x 10 super(-5), 1.6 x 10 super(-5) for J = 0, 1, and 2, respectively, at the 90% confidence level. These limits are significantly lower than the central values (with uncertainties of 50% to 70%) predicted using the light cone formalism but are consistent with calculations using the nonrelativistic QCD (NRQCD) factorization approach.
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