2,952 research outputs found
Branching ratio measurements of decays
We have just entered an era of precision measurements for
Observation of Radiative Decay
We report the observation of the decay with a
statistical significance of in 78.1 \ifb of data collected by the
Belle experiment at the KEKB collider. This is the first observation
of a flavor-changing radiative decay of a charmed meson. The Cabibbo- and
color-suppressed decays , are also observed for
the first time. We measure branching fractions \br(D^{0} \to \phi \gamma)
= [ 2.60^{+0.70}_{-0.61} \stat {}^{+0.15}_{-0.17} \syst ] \times 10^{-5},
\br(D^{0} \to \phi \pi^{0})
= [ 8.01 \pm 0.26 \stat \pm 0.47 \syst ] \times 10^{-4}, and \br(D^{0} \to
\phi \eta) = [ 1.48 \pm 0.47 \stat \pm 0.09 \syst ] \times 10^{-4}.Comment: 9 pages, 4 figures, Belle Preprint 2003-24, KEK Preprint 2003-75,
updated version of BELLE-CONF-0346 (contributed paper to the XXI
International Symposium on Lepton and Photon Interactions at High
Energies,Fermilab Aug 11-16,2003). to appear in Phys. Rev. Let
Second order QCD corrections to inclusive semileptonic b \to Xc l \bar \nu_l decays with massless and massive lepton
We extend previous computations of the second order QCD corrections to
semileptonic b \to c inclusive transitions, to the case where the charged
lepton in the final state is massive. This allows accurate description of b \to
c \tau \bar \nu_\tau decays. We review techniques used in the computation of
O(\alpha_s^2) corrections to inclusive semileptonic b \to c transitions and
present extensive numerical studies of O(\alpha_s^2) QCD corrections to b \to c
l \bar \nu_l decays, for l =e, \tau.Comment: 30 pages, 4 figures, 5 table
Observation of Large CP Violation and Evidence for Direct CP Violation in B0-->pi+pi- Decays
We report the first observation of CP-violating asymmetries in B0 --> pi+pi-
decays based on a 140 fb-1 data sample collected at the Upsilon(4S) resonance
with the Belle detector at the KEKB asymmetric-energy e+e- collider. We
reconstruct one neutral B meson as a B0 --> pi+pi- CP eigenstate and identify
the flavor of the accompanying B meson from its decay products. We apply an
unbinned maximum likelihood fit to the distribution of the time intervals
between the two B meson decay points. The fit yields the CP-violating asymmetry
amplitudes Apipi = +0.58+/-0.15(stat)+/-0.07(syst) and Spipi =
-1.00+/-0.21(stat)+/-0.07(syst). We rule out the CP-conserving case,
Apipi=Spipi=0, at a level of 5.2 standard deviations. We also find evidence for
direct CP violation with a significance at or greater than 3.2 standard
deviations for any Spipi value.Comment: 9 pages, 3 figure
An Upper Bound on the Decay tau -> mu gamma from Belle
We have performed a search for the lepton-flavor-violating decay tau -> mu
gamma using a data sample of 86.3fb^{-1} accumulated by the Belle detector at
KEK. No evidence for a signal is seen, and we set an upper limit for the
branching fraction of B(tau -> mu gamma) < 3.1 x 10^{-7} at the 90% confidence
level.Comment: 6 pages, 4 figuresm, submitted to Phys. Rev. Let
Observation of a narrow charmonium-like state in exclusive B+ -> K+ pi+pi- J/psi decays
We report the observation of a narrow charmonium-like state produced in the
exclusive decay process B+ -> K+ pi+pi- J/psi. This state, which decays into
pi+pi- J/psi, has a mass of 3872.0+-0.6(stat)+-0.5(syst) MeV, a value that is
very near the M_D + M_D* mass threshold. The results are based on an analysis
of 152M B-Bbar events collected at the Upsilon(4S) resonance in the Belle
detector at the KEKB collider. The statistical significance of the signal is in
excess of 10 sigma.Comment: 10 pages 4 figures, submitted to Physical Review Letter
Observation of B+ to Lambda Lambdabar K+
We report the first observation of the charmless hyperonic B decay, B^+ -->
Lambda Lambdabar K^+, using a 140 fb^-1 data sample recorded at the Upsilon(4S)
resonance with the Belle detector at the KEKB e^+e^- collider. The measured
branching fraction is B(B^+ --> Lambda Lambdabar K^+) = 2.91 ^{+0.90}_{-0.70}
+/- 0.38 *10^-6 . We also perform a search for the related decay mode B^+ -->
Lambda Lambdabar pi^+, but do not find a significant signal. We set a 90%
confidence-level upper limit of B(B^+ --> Lambda Lambdabar pi^+) < 2.8 * 10^-6.Comment: 9 pages, 3 figures, submitted to Phys. Rev. Let
Observation of B+ -> p pbar pi+, B0 -> p pbar K0, and B+ -> p pbar K*+
We report the first observation of a b -> u type charmless baryonic B decay,
B+ -> p pbar pi+, as well as b -> s type B0 -> p pbar K0 and B+ -> p pbar K*+
decays. The analysis is based on a 78fb^{-1} data sample recorded on the
Upsilon(4S) resonance with the Belle detector at KEKB. We find BF(B+ -> p pbar
pi+) = (3.06^{+0.73}_{-0.62} \pm 0.37)*10^{-6}, BF(B0 -> p pbar K0)
=(1.88^{+0.77}_{-0.60} \pm 0.23)*10^{-6}, and BF(B+ -> p pbar K*+) =
(10.3^{+3.6 + 1.3}_{-2.8 -1.7})*10^{-6}. We also update BF(B+ -> p pbar K+) =
(5.66^{+0.67}_{-0.57} \pm 0.62)* 10^{-6}, and present an upper limit on BF(B0
-> p pbar K*0) at the 90% confidence level. A common feature of the observed
decay modes is threshold peaking in baryon pair invariant mass.Comment: 10 pages, 12 figure file
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