We present a search for the decays B+→μ+νμ and B+→e+νe in a 253 fb−1 data sample collected at the ϒ(4S) resonance with the Belle detector at the KEKB asymmetric-energy B factory. We find no ...significant evidence for a signal and set 90% confidence level upper limits of B(B+→μ+νμ)<1.7×10−6 and B(B+→e+νe)<9.8×10−7.
We report measurements of partial branching fractions of inclusive charmless semileptonic B-meson decays at the endpoint of the electron momentum spectrum. The measurements are made in six ...overlapping momentum intervals that have lower bounds ranging from 1.9 to 2.4 GeV/c and a common upper bound of 2.6 GeV/c, as measured in the centre of mass frame. The results are based on a sample of 29 million BB¯ pairs, accumulated by the Belle detector at the KEKB asymmetric e+e− collider operating on the ϒ(4S) resonance. In the momentum interval ranging from 1.9 to 2.6 GeV/c we measure the partial branching fraction ΔB(B→Xueνe)=(8.47±0.37±1.53)×10−4, where the first error is statistical and the second is systematic. A prediction of the partial rate R=(21.69±3.62−1.98+2.18)|Vub|2 ps−1 in this momentum interval based on theory is calculated with input HQET parameters that have been derived from Belle's measurement of the B→Xsγ photon energy spectrum, where the first error is due to the uncertainty on HQET parameters and the second error is from theory. Using both ΔB(B→Xueνe) and R we find |Vub|=(5.08±0.47±0.42−0.23+0.26)×10−3, where the first error is from the partial branching fraction, and the second and third errors are from uncertainties in R.
A high precision study of the process γγ→pp¯ has been performed using a data sample of 89 fb−1 collected with the Belle detector at the KEKB e+e− collider. The cross section of pp¯ production has ...been measured at two-photon center-of-mass (c.m.) energies between 2.025 and 4.0 GeV and in the c.m. angular range of |cosθ∗|<0.6. Production of γγ→ηc→pp¯ is observed and the product of the two-photon width of the ηc and its branching ratio to pp¯ is determined.
We have searched for neutrinoless τ lepton decays into three charged leptons using an 87.1fb−1 data sample collected with the Belle detector at the KEKB e+e− collider. Since the number of signal ...candidate events is compatible with that expected from the background, we set 90% confidence level upper limits on the branching fractions in the range (1.9–3.5)×10−7 for various decay modes τ−→ℓ−ℓ+ℓ− where ℓ represents e or μ.
We present the first observation of τ lepton decays to hadronic final states with a ϕ-meson. This analysis is based on 401 fb−1 of data accumulated at the Belle experiment. The branching fraction ...obtained is B(τ−→ϕK−ντ)=(4.05±0.25±0.26)×10−5.
We have measured the branching fractions for the exclusive decay modes B→χc1(2)K(K∗) using a 140 fb−1 data sample collected by the Belle detector at the KEKB asymmetric-energy e+e− collider. The ...measured branching fractions for B+→χc1K+, B0→χc1K0, B0→χc1K∗0 and B+→χc1K∗+ decay modes are (4.5±0.2±0.5)×10−4, (3.5±0.3±0.5)×10−4, (3.1±0.3±0.7)×10−4 and (4.1±0.6±0.9)×10−4, respectively, where the first error is statistical and the second error is systematic. We do not observe statistically significant signals for the B→χc2K(K∗) decay modes and set upper limits at the 90% confidence level. We also study the helicity distribution for B→χc1K∗ decay mode and show that the longitudinal polarization component is dominant.
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