235 research outputs found
Determination of the Michel Parameters rho, xi, and delta in tau-Lepton Decays with tau --> rho nu Tags
Using the ARGUS detector at the storage ring DORIS II, we have
measured the Michel parameters , , and for
decays in -pair events produced at
center of mass energies in the region of the resonances. Using
as spin analyzing tags, we find , , , , and . In addition, we report
the combined ARGUS results on , , and using this work
und previous measurements.Comment: 10 pages, well formatted postscript can be found at
http://pktw06.phy.tu-dresden.de/iktp/pub/desy97-194.p
Search for Decays at Belle
We present a search for the B-> pi e^+ e^- and B-> pi \mu^+ \mu^- decays,
with a data sample of 657 million BBbar pairs collected with the Belle detector
at the KEKB collider. Signal events are reconstructed from a charged
or a neutral pion candidate and a pair of oppositely charged electrons or
muons. No significant signal is observed and we set the upper limit on the
isospin-averaged branching fraction BF(B -> \pi \ell^+\ell^-) < 6.2x10^-8 at
the 90% confidence level.Comment: 8 pages, 3 figures, accepted by PRD(RC
Evidence for B- -> tau- nu_bar with a Semileptonic Tagging Method
We present a measurement of the decay B- -> tau- nu_bar using a data sample
containing 657 million BB_bar pairs collected at the Upsilon(4S) resonance with
the Belle detector at the KEKB asymmetric-energy e+e- collider. A sample of
BB_bar pairs are tagged by reconstructing one B meson decaying
semileptonically. We detect the B- -> tau- nu_bar candidate in the recoil. We
obtain a signal with a significance of 3.6 standard deviations including
systematic uncertainties, and measure the branching fraction to be Br(B- ->
tau- nu_bar) = [1.54+0.38-0.37(stat)+0.29-0.31(syst)]*10^-4. This result
confirms the evidence for B- -> tau- nu_bar obtained in a previous Belle
measurement that used a hadronic B tagging method.Comment: 7 pages, 3 figures, corrected references, to appear in PRD-R
Search for leptonic decays of D0 mesons
We search for the flavor-changing neutral current decays D0\to mu+mu- and
D0\to e+e-, and for the lepton-flavor violating decays D0\to e\pm mu\mp using
660 fb^-1 of data collected with the Belle detector at the KEKB
asymmetric-energy e+e- collider. We find no evidence for any of these decays.
We obtain significantly improved upper limits on the branching fractions:
B(D0\to mu+mu-)<1.4x10-7, B(D0\to e+e-)<7.9x10-8, and B(D0\to e+mu-)+B(D0\to
mu+e-)<2.6x10-7 at 90% confidence level.Comment: 6 pages, 3 figure
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
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
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
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
Time-dependent CP Asymmetries in Decays
We report the first measurement of CP-violation parameters in B^0 ->
K_S^0\rho^0\gamma decays based on 657 million B\bar B pairs collected with the
Belle detector at the KEKB asymmetric-energy collider. We measure the
time-dependent CP violating parameter S_{K_S^0\rho^0\gamma}= 0.11 +/-
0.33(stat.)^{+0.05}_{-0.09}(syst.). We also obtain the effective direct CP
violating parameter A_eff=0.05 +/- 0.18(stat.) +/- 0.06(syst.) for
m_{K_S\pi^+\pi^-}<1.8 GeV/c^2 and 0.6 GeV/c^2<m_{\pi^+\pi^-}<0.9 GeV/c^2.Comment: 6 pages, 3 figures, to be submitted to PR
Dalitz analysis of B --> K pi psi' decays and the Z(4430)+
From a Dalitz plot analysis of B --> K pi psi' decays, we find a signal for
Z(4430)+ --> pi+ psi' with a mass M= (4443(+15-12)(+19-13))MeV/c^2, width
Gamma= (107(+86-43)(+74-56))MeV, product branching fraction BR(B0 --> K-
Z(4430)+) x BR(Z(4430)+ --> pi+ psi')= (3.2(+1.8-0.9)(+5.3-1.6)) x 10^{-5}, and
significance of 6.4sigma that agrees with previous Belle measurements based on
the same data sample. In addition, we determine the branching fraction BR(B^0
--> K*(892)^0 psi')= (5.52(+0.35-0.32)(+0.53-0.58)) x 10^{-4} and the fraction
of K*(892)^0 mesons that are longitudinally polarized f_L=
44.8(+4.0-2.7)(+4.0-5.3)%. These results are obtained from a 605fb^{-1} data
sample that contains 657 million B-anti-B pairs collected near the Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric energy e+e- collider.Comment: Final version published in PRD(RC
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