71 research outputs found
Observation of Cabibbo-suppressed and W-exchange Lambda_c^+ baryon decays
We present measurements of the Cabibbo-suppressed decays Lambda_c^+ -->
Lambda0 K+ and Lambda_c^+ --> Sigma0 K+ (both first observations), Lambda_c^+
--> Sigma+ K+ pi- (seen with large statistics for the first time), Lambda_c^+
--> p K+ K- and Lambda_c^+ --> p phi (measured with improved accuracy).
Improved branching ratio measurements for the decays Lambda_c^+ --> Sigma+ K+
K- and Lambda_c^+ --> Sigma+ phi, which are attributed to W-exchange diagrams,
are shown. We also present the first evidence for Lambda_c^+ --> Xi(1690)^0 K+
and set an upper limit on the non-resonant decay Lambda_c^+ --> Sigma+ K+ K-.
This analysis was performed using 32.6 fb^{-1} of data collected by the Belle
detector at the asymmetric e+ e- collider KEKB.Comment: Submitted to Phys. Lett. B. v2: A small correction to the Authorlist
was made. An earlier version of this analysis was released as
BELLE-CONF-0130, hep-ex/010800
Search for Direct CP Violation in B -> K pi Decays
We search for direct CP violation in flavor specific B -> K pi decays by
measuring the rate asymmetry between charge conjugate modes. The search is
performed on a data sample of 11.1 million B B bar events recorded on the
Upsilon(4S) resonance by the Belle experiment at KEKB. We measure 90%
confidence intervals in the partial rate asymmetry A_CP of -0.25 < A_CP(K-/+
pi+/-) < 0.37, -0.40 < A_CP(K-/+ pi^0) < 0.36, and -0.53 < A_CP(K^0 pi-/+) <
0.82. By combining the K-/+ pi+/- and K-/+ pi^0 final states, we conclude that
-0.22 < A_CP[K-/+(pi+/- + pi^0)] < 0.25 at the 90% confidence level.Comment: Submitted to PRD Rapid Communication
Observation of Large CP Violation in the Neutral B Meson System
We present a measurement of the Standard Model CP violation parameter sin
2phi_1 based on a 29.1 fb^{-1} data sample collected at the Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.
One neutral B meson is fully reconstructed as a J/psi Ks, psi(2S) Ks, chi_c1
Ks, eta_c Ks, J/psi K_L or J/psi K^{*0} decay and the flavor of the
accompanying B meson is identified from its decay products. From the asymmetry
in the distribution of the time intervals between the two B meson decay points,
we determine sin 2phi_1 = 0.99 +- 0.14(stat) +- 0.06(syst). We conclude that we
have observed CP violation in the neutral B meson system.Comment: 4 figures, to appear in Phys. Rev. Letter
Measurement of the Branching Fraction for B->eta' K and Search for B->eta'pi+
We report measurements for two-body charmless B decays with an eta' meson in
the final state. Using 11.1X10^6 BBbar pairs collected with the Belle detector,
we find BF(B^+ ->eta'K^+)=(79^+12_-11 +-9)x10^-6 and BF(B^0 ->
eta'K^0)=(55^+19_-16 +-8)x10^-6, where the first and second errors are
statistical and systematic, respectively. No signal is observed in the mode B^+
-> eta' pi^+, and we set a 90% confidence level upper limit of BF(B^+->
eta'pi^+) eta'K^+- decays is
investigated and a limit at 90% confidence level of -0.20<Acp<0.32 is obtained.Comment: Submitted to Physics Letters
A Measurement of Lifetime Difference in Meson Decays
We report a measurement of the - mixing parameter
using 23.4 fb of data collected near the (4S) resonance with
the Belle detector at KEKB. is measured from the lifetime difference
of mesons decaying into the state and the CP even eigenstate
. We find , where
the first error is statistical and the second systematic, corresponding to a
95% confidence interval .Comment: 10 pages, 3 figure
Search for Charmless Two-body Baryonic Decays of B Mesons
We report the results of a search for the rare baryonic decays , , and . The analysis
is based on a data set of events collected by the
Belle detector at the KEKB collider. No statistically significant
signals are found, and we set branching fraction upper limits , , and at the 90% confidence level.Comment: 6 pages, 4 figures and 1 table. Submitted to Phys. Rev. D Rapid
Communication
Observation of chi_c2 Production in B-meson Decay
We report the first observation of chi_c2 production in B-meson decays. We
find an inclusive B -> chi_c2 X branching fraction of (1.80^{+0.23}_{-0.28}+/-
0.26) 10^-3. The data set, collected with the Belle detector at the KEKB e^+e^-
collider, consists of 31.9 million B\bar B events. We also present branching
fractions and momentum spectra for both chi_c1 and chi_c2 production.Comment: 5 pages with 2 figure
Precise Measurement of B Meson Lifetimes with Hadronic Decay Final States
The lifetimes of the B0bar and B- mesons are extracted from 29.1/fb of data
collected with the Belle detector at the KEK B-factory. A fit to the decay
length differences of neutral and charged B meson pairs, measured in events
where one of the B mesons is fully reconstructed in several hadronic modes,
yields tau_B0bar = 1.554 +/- 0.030(stat) +/- 0.019(syst) ps, tau_B- = 1.695 +/-
0.026(stat) +/- 0.015(syst) ps, and tau_B-/tau_B0bar = 1.091 +/- 0.023(stat)
+/- 0.014(syst).Comment: 10 pages, 2 figures, and 1 table. (To be) published in Phys. Rev.
Let
Observation of Mixing-induced CP Violation in the Neutral B Meson System
This report describes an observation of mixing-induced CP violation and a
measurement of the CP violation parameter, sin(2phi_1), with the Belle detector
at the KEKB asymmetric e+e- collider. Using a data sample of 29.1 fb-1 recorded
on the Upsilon(4S) resonance that contains 31.3 million BBbar pairs, we
reconstruct decays of neutral B mesons to the following CP eigenstates: J/psi
K_S^0, psi(2S) K_S^0, chi_c1 K_S^0, eta_c K_S^0, J/psi K_L^0 and J/psi K^*0.
The flavor of the accompanying B meson is identified by combining information
from primary and secondary leptons, K+/- mesons, lambda baryons, slow and fast
pions. The proper-time interval between the two B meson decays is determined
from the distance between the two decay vertices measured with a silicon vertex
detector. The result sin(2phi_1) = 0.99 +/- 0.14(stat) +/- 0.06(syst) is
obtained by applying a maximum likelihood fit to the 1137 candidate events. We
conclude that there is large CP violation in the neutral B meson system. A zero
value for sin(2phi_1) is ruled out by more than six standard deviations.Comment: 25 pages, 16 figures, accepted for publication in Physical Review
Production of Prompt Charmonia in Annihilation at GeV
The production of prompt , , and is
studied using a data sample collected with the Belle detector at
the and 60 MeV below the resonance. The yield of prompt
mesons in the sample is compatible with that of continuum
production; we set an upper limit at the 95% confidence level, and find pb. The cross-sections for prompt
and direct are measured. The momentum spectrum, production
angle distribution and polarization are studied.Comment: submitted to Phys. Rev. Let
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