43 research outputs found
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
Moments of the Hadronic Invariant Mass Spectrum in B --> X_c l nu Decays at Belle
We present a measurement of the hadronic invariant mass squared (M^2_X)
spectrum in charmed semileptonic B meson decays B --> X_c l nu based on 140
fb^-1 of Belle data collected near the Y(4S) resonance. We determine the first,
the second central and the second non-central moments of this spectrum for
lepton energy thresholds ranging between 0.7 and 1.9 GeV. Full correlations
between these measurements are evaluated.Comment: published version of the paper (one figure added, minor changes in
the text); 16 pages, 3 figures, 10 table
Search for new charmonium states in the processes e+ e- --> J/psi D(*) D(*) at sqrt{s} ~ 10.6 GeV
We present a study of the X(3940) state in the process e+e- -> J/psi D* Dbar.
The X(3940) mass and width are measured to be (3942 +7 -6 +- 6)MeV/c^2 and
Gamma=(37 + 26 - 15 +- 8 MeV. In the process e+e- -> J/psi D* D*bar we have
observed another charmonium-like state, which we denote as X(4160), in the
spectrum of invariant masses of D*+ D*- combinations. The X(4160) parameters
are M= 4156 + 25 - 20 +- 15 MeV/c^2 and Gamma = 139 + 111 -61 +- 21 MeV. The
analysis is based on a data sample with an integrated luminosity of 693 /fb
recorded near the Upsilon(4S) resonance with the Belle detector at the KEKB e+
e- asymmetric-energy collider.Comment: 7 pages, 2 figures Contribution paper for conferences EPS2007 and
Lepton Photon 2007, Belle-Conference-070
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
Precise Measurements of Beam Spin Asymmetries in Semi-Inclusive production
We present studies of single-spin asymmetries for neutral pion
electroproduction in semi-inclusive deep-inelastic scattering of 5.776 GeV
polarized electrons from an unpolarized hydrogen target, using the CEBAF Large
Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator
Facility. A substantial amplitude has been measured in the
distribution of the cross section asymmetry as a function of the azimuthal
angle of the produced neutral pion. The dependence of this amplitude
on Bjorken and on the pion transverse momentum is extracted with
significantly higher precision than previous data and is compared to model
calculations.Comment: to be submitted PL
Observation of the Decay \bar{B0}-> Ds+ Lambda \bar{p}
We report the first observation of the decay \bar{B0} -> D_s^+ Lambda \bar{p}
with a statistical significance of 6.6 sigma. We measure Br(\bar{B0} -> Ds+
Lambda \bar{p}) = (2.9 \pm 0.7\pm 0.5 \pm 0.4)* 10^{-5}, where the first error
is statistical, the second is systematic and the third error comes fr\om the
uncertainty in Br(Ds+ -> phi pi+). The data used for this analysis was
accumulated at the Upsilon(4S) resonance, using the Belle detector at the KEKB
asymmetric-energy e+e- collider. The integrated luminosity of the data sample
is 414 fb-1, corresponding to 449*10^{6} B{\bar B} pairs.Comment: 5 pages, 2 PostScript figures, 1 tabl
Evidence for Neutral B Meson Decays to wK*0
We present the results of a study of the charmless vector-vector decay
B0->wK*0 with 657x10^6 BB(bar) pairs collected with the Belle detector at the
KEKB e+e- collider. We measure the branching fraction to be
B(B0->wK*0)=[1.8+/-0.7(stat)+/-0.3(syst)]x10^-6 with 3.0sigma significance. We
also perform a helicity analysis of the w and K*0 vector mesons, and obtain the
longitudinal polarization fraction
fL(B0->wK*0)=0.56+/-0.29(stat)+0.18-0.08(syst). Finally, we measure a large
non-resonant branching fraction B[B->wK+pi-; M(Kpi)\in(0.755,1.250)
GeV/c^2]=[5.1+/-0.7(stat)+/-0.7(syst)]x10^-6 with a significance of 9.5sigma.Comment: 6 pages, 3 figures (7 figure files
Measurement of B(Ds -> munu)
We present a measurement of the branching fraction
using a 548 fb data sample collected by the Belle experiment at the KEKB
collider. The momentum is determined by reconstruction of the
system recoiling against in events of the type , where represents additional pions or photons
from fragmentation. The full reconstruction method provides high resolution in
the neutrino momentum and thus good background separation, equivalent to that
reached by experiments at the tau-charm factories. We obtain the branching
fraction , implying a decay constant of MeV.Comment: 6 pages, 2 figures, replaced by version subm. to Phys. Rev. Let
Study of the decay mechanism for B+ to p pbar K+ and B+ to p pbar pi+
We study the characteristics of the low mass ppbar enhancements near
threshold in the three-body decays B+ to p pbar K+ and B+ to p pbar pi+. We
observe that the proton polar angle distributions in the ppbar helicity frame
in the two decays have the opposite polarity, and measure the forward-backward
asymmetries as a function of the ppbar mass for the p pbar K+ mode. We also
search for the intermediate two-body decays, B+ to pbar Delta++ and B+ to p
Delta0bar, and set upper limits on their branching fractions. These results are
obtained from a 414 fb^{-1} data sample that contains 449 times 10^6 BBbar
events collected near the Upsilon(4S) resonance with the Belle detector at the
KEKB asymmetric-energy e+ e- collider.Comment: 15 pages, 5 figures (14 figure files), revisions to Phys. Lett.