46 research outputs found
Search for Resonant Decays at Belle
We report measurements and searches for resonant decays where is a
meson or
the X(3872) particle.Comment: accepted by Physics Letters
Study of charmonia in four-meson final states produced in two-photon collisions
We report measurements of charmonia produced in two-photon collisions and
decaying to four-meson final states, where the meson is either a charged pion
or a charged kaon. The analysis is based on a 395fb^{-1} data sample
accumulated with the Belle detector at the KEKB electron-positron collider. We
observe signals for the three C-even charmonia eta_c(1S), chi_{c0}(1P) and
chi_{c2}(1P) in the pi^+pi^-pi^+pi^-, K^+K^-pi^+pi^- and K^+K^-K^+K^- decay
modes. No clear signals for eta_c(2S) production are found in these decay
modes. We have also studied resonant structures in charmonium decays to
two-body intermediate meson resonances. We report the products of the
two-photon decay width and the branching fractions, Gamma_{gamma gamma}B, for
each of the charmonium decay modes.Comment: 22 pages, 12 figure
Improved measurement of CP-violating parameters in rho+rho- decays
We present a measurement of the CP-violating asymmetry in rho+rho- decays
using 535 million BBbar pairs collected with the Belle detector at the KEKB
e+e- collider. We measure CP-violating coefficients A = 0.16 +- 0.21(stat) +-
0.07 (syst) and S = 0.19 +- 0.30(stat) +- 0.07 (syst}. These values are used to
determine the unitarity triangle angle phi_2 using an isospin analysis; the
solution consistent with Standard Model lies in the range 53 < phi_2 < 114 deg.
at 90 C.L.Comment: 6 pages, 4 figures, presented at JPS/DPF 2006 (Added KEK, BELLE
preprint numbers, submitted to PRD(RC)
Search for the Electric Dipole Moment of the tau Lepton
We have searched for a CP violation signature arising from an electric dipole
moment (d_tau) of the tau lepton in the e+e- -> tau+tau- reaction. Using an
optimal observable method and 29.5 fb^{-1} of data collected with the Belle
detector at the KEKB collider at sqrt{s} = 10.58 GeV, we find Re(d_tau) = (1.15
+- 1.70) x 10^{-17} ecm and Im(d_tau) = (-0.83 +- 0.86) x 10^{-17} ecm and set
the 95% confidence level limits -2.2 < Re(d_tau) < 4.5 (10^{-17}ecm) and -2.5 <
Im(d_tau) < 0.8 (10^{-17}ecm).Comment: 15 pages, LaTeX, 21 figures, submitted to Phys. Lett.
Search for tau -> e gamma decay at Belle
We have searched for the lepton-flavor-violating decay tau -> e gamma using a
data sample of 86.7/fb collected with the Belle detector at the KEKB asymmetric
e^+ e^- collider. No evidence for a signal is obtained, and we set an upper
limit for the branching fraction Br(tau -> e gamma) < 3.9 x 10^-7 at the 90%
C.L.Comment: 11 pages, 10 figures, ReVTeX4, eps
Search for B -> h(*) nu nubar Decays at Belle
We present a search for the rare decays B -> h(*) nu nubar, where h(*) stands
for a light meson. A data sample of 535 million BBbar pairs collected with the
Belle detector at the KEKB e+e- collider is used. Signal candidates are
required to have an accompanying B meson fully reconstructed in a hadronic mode
and signal-side particles consistent with a single h(*) meson. No significant
signal is observed and we set upper limits on the branching fractions at 90%
confidence level. The limits on B0 -> K*0 nu nubar and B+ -> K+ nu nubar decays
are more stringent than the previous constraints, while the first searches for
B0 -> K0 nu nubar, pi0 nu nubar, rho0 nu nubar, phi nu nubar and B+ -> K*+ nu
nubar, rho+ nu nubar are reported.Comment: 6 pages, 2 figures, submit to PR
Measurement of the gamma gamma -> pi+ pi- and gamma gamma -> K+ K- processes at energies of 2.4 - 4.1 GeV
We have measured pi+pi- and K+K- production in two-photon collisions using
87.7 /fb of data collected with the Belle detector at the asymmetric energy
e+e- collider KEKB. The cross sections are measured to high precision in the
two-photon center-of-mass energy (W) range between 2.4 GeV < W < 4.1 GeV and
angular region |cos theta^{*}| < 0.6. The cross section ratio
sigma(gammagamma->K+K-)/sigma(gammagamma->pi+pi-) is measured to be 0.89 +-
0.04(stat) +- 0.15(syst) in the range of 3.0 GeV < W < 4.1 GeV, where the ratio
is energy independent. We observe a sin^{-4} theta^{*} behavior of the cross
section in the same W range. Production of chi_{c0} and chi_{c2} mesons is
observed in both gammagamma -> pi+pi- and gammagamma -> K+K- modes.Comment: 17 pages, 5 figures, submitted to Phys. Lett. B, errors relative to
the two-photon decay width correcte
Photoproduction of mesons associated with a leading neutron
The photoproduction of mesons associated with a leading
neutron has been observed with the ZEUS detector in collisions at HERA
using an integrated luminosity of 80 pb. The neutron carries a large
fraction, {}, of the incoming proton beam energy and is detected at
very small production angles, { mrad}, an indication of
peripheral scattering. The meson is centrally produced with
pseudorapidity {
GeV}, which is large compared to the average transverse momentum of the neutron
of 0.22 GeV. The ratio of neutron-tagged to inclusive production is
in the photon-proton
center-of-mass energy range { GeV}. The data suggest that the
presence of a hard scale enhances the fraction of events with a leading neutron
in the final state.Comment: 28 pages, 4 figures, 2 table
Search for contact interactions, large extra dimensions and finite quark radius in ep collisions at HERA
A search for physics beyond the Standard Model has been performed with
high-Q^2 neutral current deep inelastic scattering events recorded with the
ZEUS detector at HERA. Two data sets, e^+ p \to e^+ X and e^- p \to e^- X, with
respective integrated luminosities of 112 pb^-1 and 16 pb^-1, were analyzed.
The data reach Q^2 values as high as 40000 GeV^2. No significant deviations
from Standard Model predictions were observed. Limits were derived on the
effective mass scale in eeqq contact interactions, the ratio of leptoquark mass
to the Yukawa coupling for heavy leptoquark models and the mass scale parameter
in models with large extra dimensions. The limit on the quark charge radius, in
the classical form factor approximation, is 0.85 10^-16 cm.Comment: 28 pages, 4 figures, accepted for publication in Physics Letters
Isolated tau leptons in events with large missing transverse momentum at HERA
A search for events containing isolated tau leptons and large missing
transverse momentum, not originating from the tau decay, has been performed
with the ZEUS detector at the electron-proton collider HERA, using 130 pb^-1 of
integrated luminosity. A search was made for isolated tracks coming from
hadronic tau decays. Observables based on the internal jet structure were
exploited to discriminate between tau decays and quark- or gluon-induced jets.
Three tau candidates were found, while 0.40 +0.12 -0.13 were expected from
Standard Model processes, such as charged current deep inelastic scattering and
single W-boson production. To search for heavy-particle decays, a more
restrictive selection was applied to isolate tau leptons produced together with
a hadronic final state with high transverse momentum. Two candidate events
survive, while 0.20 +-0.05 events are expected from Standard Model processes.Comment: 28 pages, 4 figures, 3 tables, accepted by Phys. Lett. B. Updated
with minor changes to the text requested by the journal refere