176 research outputs found
Measurement Of |V_ub| From Inclusive Charmless Semileptonic B Decays
We present the partial branching fraction for inclusive charmless
semileptonic B decays and the corresponding value of the CKM matrix element
|Vub|, using a multivariate analysis method to access ~90% of the B -> Xu l nu
phase space. This approach dramatically reduces the theoretical uncertainties
from the b-quark mass and non-perturbative QCD compared to all previous
inclusive measurements. The results are based on a sample of 657 million B
-Bbar pairs collected with the Belle detector. We find that Delta BR(B -> Xu l
nu; p^*B_l>1.0 GeV/c=1.963 x (1 +/- 0.088(stat.) +/- 0.081(sys.)) x 10^-3.
Corresponding values of |Vub| are extracted using several theoretical
calculations.Comment: 9 pages, 1 figure, 2 tables. Published in PR
Observation of anomalous Upsilon(1S)pi+pi- and Upsilon(2S)pi+pi- production near the Upsilon(5S) resonance
We report the first observation of e+e- -> Upsilon(1S)pi+pi-,
Upsilon(2S)pi+pi-, and first evidence for e+e- -> Upsilon(3S)pi+pi-,
Upsilon(1S)K+K-, near the peak of the Upsilon(5S) resonance at sqrt{s}~10.87
GeV. The results are based on a data sample of 21.7 fb^-1 collected with the
Belle detector at the KEKB e+e- collider. Attributing the signals to the
Upsilon(5S) resonance, the partial widths Gamma(Upsilon(5S) -> Upsilon(1S)
pi+pi-) = 0.59 +- 0.04 (stat) +- 0.09 (syst) MeV and Gamma(Upsilon(5S) ->
Upsilon(2S) pi+pi-) = 0.85 +- 0.07 (stat) +- 0.16 (syst) MeV are obtained from
the observed cross sections. These values exceed by more than two orders of
magnitude the previously measured partial widths for dipion transitions between
lower Upsilon resonances.Comment: 6 pages, 4 figures, submit to PR
Observation of B+ -> Dbar*0 tau+ nu_tau and Evidence for B+ -> Dbar^0 tau+ nu_tau at Belle
We present measurements of B+ -> Dbar*0 tau+ nu_tau and B+ -> Dbar^0 tau+
nu_tau decays in a data sample of 657 x 10^6 BBbar pairs collected with the
Belle detector at the KEKB asymmetric-energy e+e- collider. We find
446^{+58}_{-56} events of the decay B+ -> Dbar*0 tau+ nu_tau with a
significance of 8.1 standard deviations, and 146^{+42}_{-41} events of the
decay B+ -> Dbar0 tau+ nu_tau with a significance of 3.5 standard deviations.
The latter signal provides the first evidence for this decay mode. The measured
branching fractions are B(B+ -> Dbar*0 tau+ nu_tau)=(2.12^{+0.28}_{-0.27}
(stat) +- 0.29 (syst)) % and B(B+ -> Dbar0 tau+ nu_tau)=(0.77 +- 0.22 (stat) +-
0.12 (syst)) %.Comment: 6 pages, 4 figures, submitted to Phys. Rev. Let
Study of the suppressed B meson decay B^- -> D K^-, D -> K^+ \pi^-
We report a study of the suppressed B meson decay B^- -> D K^- followed by D
-> K^+ \pi^-, where D indicates a D^0 or \bar{D}^0 state. The two decay paths
interfere and provide information on the CP-violating angle \phi_3. We use a
data sample containing 657 x 10^6 B\bar{B} pairs recorded at the \Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- storage
ring. We do not find significant evidence for the mode B^- -> D K^-, D -> K^+
\pi^-, and set an upper limit of r_B < 0.19, where r_B is the magnitude of the
ratio of amplitudes |A(B^- -> \bar{D}^0 K^-)/A(B^- -> D^0 K^-)|. The decay B^-
-> D \pi^-, D -> K^+ \pi^- is also analyzed as a reference, for which we
observe a signal with 6.6\sigma significance, and measure the charge asymmetry
A_{D\pi} to be -0.02^{+0.15}_{-0.16}(stat) \pm 0.04(syst). In addition, the
ratio B(B^- -> D^0 K^-)/B(B^- -> D^0 \pi^-) is measured to be [6.77 \pm
0.23(stat) \pm 0.30(syst)] x 10^{-2}.Comment: 6 pages, 3 figures, 2 table
Measurement of CP violating asymmetries in B^0 -> K^+K^- K^0_S decays with a time-dependent Dalitz approach
We report a measurement of violating asymmetries in decays with a time-dependent Dalitz approach. This analysis
is based on a data sample of pairs accumulated
at the resonance with the Belle detector at the KEKB
asymmetric-energy collider. As the result of an unbinned maximum
likelihood fit to the selected candidates, the mixing-induced and direct
violation parameters, and are obtained for
, and other decays. We find four solutions that describe the data. There are
\{eqnarray*} \phi_1^{\rm eff}(B^0\to \phi(1020) K^0_S) & = & (32.2 \pm 9.0 \pm
2.6 \pm 1.4)^{\circ}; \phi_1^{\rm eff}(B^0\to \phi(1020) K^0_S) & = & (26.2 \pm
8.8 \pm 2.7 \pm 1.2)^{\circ};\\ \phi_1^{\rm eff}(B^0\to \phi(1020) K^0_S) & = &
(27.3 \pm 8.6 \pm 2.8 \pm 1.3)^{\circ}\; {\rm and}\\ \phi_1^{\rm eff}(B^0\to
\phi(1020) K^0_S) & = & (24.3 \pm 8.0 \pm 2.9 \pm 5.2)^{\circ}.{eqnarray*}\ The
values for the violating phase in are similar
but other properties of the Dalitz plot are quite different for the four
solutions. These four solutions have consistent values for
all three meson decay channels and none of them deviates significantly from
the values measured in decays with the currently
available statistics. In addition, we find no significant direct
violation.Comment: submitted to PR
Time-Dependent CP Asymmetries in B0 -> Ks pi0 gamma transitions
We report measurements of CP violation parameters in B0->Ks pi0 gamma
transitions based on a data sample of 535x10^6 BB pairs collected with the
Belle detector at the KEKB asymmetric-energy e+ e- collider. One neutral B
meson is fully reconstructed in the B0->Ks pi0 gamma mode. The flavor of the
accompanying B meson is identified from its decay products. For a Ks pi0
invariant mass up to 1.8 GeV/c^2, we obtain S = -0.10 +- 0.31 +- 0.07 and A =
-0.20 +- 0.20 +- 0.06. For a Ks pi0 invariant mass near the K*0(892) resonance,
we obtain S = -0.32 +0.36-0.33 +-0.05 and A=-0.20 +-0.24 +-0.05.Comment: 6 pages, 3 figures, accepted by PR
Observation of B0 to p pbar K*0 with a large K*0 polarization
We observe the decay B0 to p pbar K*0 with a branching fraction of
(1.18^{+0.29}_{-0.25} (stat.) \pm 0.11 (syst.)) \times 10^{-6}. The statistical
significance is 7.2 sigma for the signal in the low ppbar mass region. We study
the decay dynamics of B0 to p pbar K*0 and compare it with B+ to p pbar K*+.
The K*0 meson is found to be almost 100% polarized (with a fraction of (101 \pm
13 \pm 3)% in the helicity zero state), while the K*+ meson has a (32 \pm 17
\pm 9)% fraction in the helicity zero state. The direct CP asymmetries for B0
to p pbar K*0 and B+ to p pbar K*+ are measured to be -0.08\pm 0.20\pm 0.02 and
-0.01\pm 0.19\pm 0.02, respectively. We also study the characteristics of the
low mass ppbar enhancements near threshold and the associated angular
distributions. In addition, we report improved measurements of the branching
fractions BF(B+ to p pbar K*+) = (3.38^{+0.73}_{-0.60} \pm 0.39) \times 10^{-6}
and BF(B0 to p pbar K0) = (2.51^{+0.35}_{-0.29} \pm 0.21) \times 10^{-6}, which
supersede our previous measurements. These results are obtained from a 492
fb^{-1} data sample collected near the Upsilon(4S) resonance with the Belle
detector at the KEKB asymmetric-energy e^+ e^- collider.Comment: 11 pages, 4 figures (8 figure files), submitted to Phys.Rev.Let
Measurement of Inclusive Radiative B-meson Decays with a Photon Energy Threshold of 1.7 GeV
Using 605/fb of data collected at the Upsilon(4S) resonance we present a
measurement of the inclusive radiative B-meson decay channel, B to X_s gamma.
For the lower photon energy thresholds of 1.7, 1.8, 1.9 and 2.0GeV, as defined
in the rest frame of the B-meson, we measure the partial branching fraction and
the mean and variance of the photon energy spectrum. At the 1.7GeV threshold we
obtain the partial branching fraction BF(B to X_s gamma) = (3.45 +/- 0.15 +/-
0.40) x 10^-4, where the errors are statistical and systematic.Comment: 9 pages, 3 figures, 2 table
Measurement of Decays and Search for
We report on a search for the decay and other charmless
modes with a final state, including
, non-resonant ,
, and . These results are obtained from a data sample containing
657 million pairs collected with the Belle detector at the KEKB
asymmetric-energy collider. We set an upper limit on
of at the 90% confidence
level (C.L.). From our measurement and an isospin
analysis, we determine the Cabibbo-Kobayashi-Maskawa phase to be degrees. We find excesses in and
non-resonant with 1.3 and 2.5 significance,
respectively. The corresponding branching fractions are less than and at the 90% C.L. In addition, we set 90% C.L.
upper limits as follows: , , and
.Comment: 6 pages, 2 figures. Submitted to PRD(RC
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