To estimate the parameters of New Physics in the future experiments, the experimental data should be compared to the cross-sections calculated in terms of some model. The values of the model ...parameters can then be extracted from the signal/background ratio (statistical significance, SS). It is shown that applying certain phase space cuts can sometimes improve the results. The ways of seeking for the ”natural” cuts in the process/model are discussed. Results for eγ→Wν→μνν are presented.
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.
It is shown that in reaction \gamma\gamma\to\ell^+\ell^-+\nu's at \sqrt{s}>200 GeV with polarized photons, large and well observable differences arise in the distribution of positive and negative ...charged leptons (\ell=\mu^\pm, e^\pm), (charge asymmetry). The modification due to the contribution of the cascade processes with intermediate \tau-lepton in \gamma \gamma \to W^\pm\ell^\mp + \nu's reaction is taken into account. This charge asymmetry is potentially sensitive to effects of physics beyond the standard model at the anticipated luminosity of the Photon Collider mode of the future international linear collider.
We report measurements and searches for resonant B±→K±h→K±γγ decays where h is a η, η′, ηc, ηc(2S), χc0, χc2, J/ψ meson or the X(3872) particle. The results are based on a data sample containing 535 ...million BB¯ pairs collected with the Belle detector at the KEKB e+e− asymmetric-energy collider operating at the ϒ(4S) resonance. Signals are observed in the modes with η and η′, and we obtain evidence for a signal in the mode with ηc. We measure B(B±→K±η→K±γγ)=(0.87−0.15+0.16(stat)−0.07+0.10(syst))×10−6, B(B±→K±η′→K±γγ)=(1.40−0.15+0.16(stat)−0.12+0.15(syst))×10−6 and B(B±→K±ηc→K±γγ)=(0.22−0.07+0.09(stat)−0.02+0.04(syst))×10−6. We set upper limits on the branching fractions of the other modes.
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.
PDF
