We report on a search for the lepton flavor violating τ−→μ−γ and τ−→e−γ decays based on 535 fb−1 of data accumulated at the Belle experiment. No signal is found and we set 90% confidence level upper ...limits on the branching ratios B(τ−→μ−γ)<4.5×10−8 and B(τ−→e−γ)<1.2×10−7.
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.
Phys.Lett.B647:67-73,2007 We present a search for the decays B+ -> mu+ nu_mu and B+ -> e+ nu_e in a 253
fb-1 data sample collected at the \Upsilon(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+ -> mu+
nu_mu) < 1.7 x 10^{-6} and B(B+ -> e+ nu_e) < 9.8 x 10^{-7}.
K
S
0
K
S
0
production in two-photon collisions has been studied using a 397.6 fb
−1 data sample collected with the Belle detector at the KEKB
e
+
e
−
collider. For the first time the cross sections ...are measured in the two-photon center-of-mass energy range between 2.4 GeV and 4.0 GeV and angular range
|
cos
θ
∗
|
<
0.6
. Combining the results with measurements of
γ
γ
→
K
+
K
−
from Belle, we observe that the cross section ratio
σ
(
K
S
0
K
S
0
)
/
σ
(
K
+
K
−
)
decreases from ∼0.13 to ∼0.01 with increasing energy. Signals for the
χ
c
0
and
χ
c
2
charmonium states are also observed.
We have searched for lepton-flavor-violating τ decays with a pseudoscalar meson (η, η′ and π0) using a data sample of 401 fb−1 collected with the Belle detector at the KEKB asymmetric-energy e+e− ...collider. No evidence for these decays is found and we set the following upper limits on the branching fractions: B(τ−→e−η)<9.2×10−8, B(τ−→μ−η)<6.5×10−8, B(τ−→e−η′)<1.6×10−7, B(τ−→μ−η′)<1.3×10−7, B(τ−→e−π0)<8.0×10−8 and B(τ−→μ−π0)<1.2×10−7 at the 90% confidence level. These results improve our previously published upper limits by factors from 2.3 to 6.3.
We report measurements of the charmless semileptonic decays B0→π−/ρ−ℓ+ν and B+→π0/ρ0ℓ+ν, based on a sample of 2.75×108BB¯ events collected at the ϒ(4S) resonance with the Belle detector at the KEKB ...e+e− asymmetric collider. In this analysis, the accompanying B meson is reconstructed in the semileptonic mode B→D(∗)ℓν, enabling detection of the signal modes with high purity. We measure the branching fractions B(B0→π−ℓ+ν)=(1.38±0.19±0.14±0.03)×10−4, B(B0→ρ−ℓ+ν)=(2.17±0.54±0.31±0.08)×10−4, B(B+→π0ℓ+ν)=(0.77±0.14±0.08±0.00)×10−4 and B(B+→ρ0ℓ+ν)=(1.33±0.23±0.17±0.05)×10−4, where the errors are statistical, experimental systematic, and systematic due to form factor uncertainties, respectively. For each mode we also present the partial branching fractions in three q2 intervals: q2<8, 8⩽q2<16, and q2⩾16 GeV2/c2. From our partial branching fractions for B→πℓν and recent results for the form factor from unquenched Lattice QCD calculations, we obtain values of the CKM matrix element |Vub|.
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