518 research outputs found
A vertical diatomic artificial molecule in the intermediate coupling regime in a parallel and perpendicular magnetic field
We present experimental results for the ground state electrochemical
potentials of a few electron semiconductor artificial molecule made by
vertically coupling two quantum dots, in the intermediate coupling regime, in
perpendicular and parallel magnetic fields up to 5 T. We perform a quantitative
analysis based on local-spin density functional theory. The agreement between
theoretical and experimental results is good, and the phase transitions are
well reproduced.Comment: Typeset using Revtex, 13 pages and 8 Postscript figure
Measurement of the branching fractions for B- --> D(*)+ pi- l- nu-bar and B0bar --> D(*)0 pi+ l- nu-bar
We report on a measurement of the branching fractions for B- --> D(*)+ pi- l-
nu-bar and B0bar --> D(*)0 pi+ l- nu-bar with 275 million BBbar events
collected at the Upsilon(4S) resonance with the Belle detector at KEKB. Events
are tagged by fully reconstructing one of the B mesons in hadronic modes. We
obtain Br(B- --> D+ pi- l- nu-bar) = (0.54 +/- 0.07(stat) +/- 0.07(syst) +/-
0.06(BR)) x 10^-2, Br(B- --> D*+ pi- l- nu-bar) = (0.67 +/- 0.11(stat) +/-
0.09(syst) +/- 0.03(BR)) x 10^-2, Br(B0bar --> D0 pi+ l- nu-bar) = (0.33 +/-
0.06(stat) +/- 0.06(syst) +/- 0.03(BR)) x 10^-2, Br(B0bar --> D*0 pi+ l-
nu-bar) = (0.65 +/- 0.12(stat) +/- 0.08(syst) +/- 0.05(BR)) x 10^-2, where the
third error comes from the error on Bbar --> D(*) l- nu-bar decays.
Contributions from B0bar --> D*+ l- nu-bar decays are excluded in the
measurement of B0bar --> D0 pi+ l- nu-bar.Comment: 6 pages, 10 figures, submitted to Physical Review D (Rapid
Communication), the Lepton-Photon 2005 Conference (Uppsala, Sweden) and the
HEP2005 Europhysics Conference (Lisboa, Portugal
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
Determination of |V_ub| from Measurements of the Inclusive Charmless Semileptonic Partial Rates of B Mesons using Full Reconstruction Tags
We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element
|V_ub|, based on 253 fb^-1 of data collected by the Belle detector at the KEKB
e^+e^- asymmetric collider. Events are tagged by fully reconstructing one of
the B mesons, produced in pairs from Upsilon(4S). The signal for b->u
semileptonic decay is distinguished from the b->c background using the hadronic
mass M_X, the leptonic invariant mass squared q^2 and the variable P_+ =
E_X-|\vec{p}_X|. The results are obtained for events with the prompt-lepton
momentum, p_l^* >= 1GeV/c, in three kinematic regions (1) M_X < 1.7 Gev/c^2,
(2) M_X 8 GeV^2/c^2, and by (3) P_+ < 0.66
GeV/c, allowing for a comparison of the three methods. The matrix element
|V_ub| is found to be (4.09+-0.19+-0.20(+0.14-0.15)+-0.18), where the errors
are statistical, systematic including Monte Carlo modeling, theoretical, and
from shape function parameter determination, respectively.Comment: 6 pages, 3 figures, 3 tables. Version as it appears in PRL. Changes
from v1: |V_ub| recalculated using mb(SF)=4.60+-0.04 and
mu_pi^2(SF)=0.20+-0.04. Title and text changed to reflect the calculation of
partial rate instead of partial Br. Fig. 3 changed. Explicit dependence of
the result on mb(SF) is give
Observation of B+->Lambda_c+Lambda_c-K+ and B0->Lambda_c+Lambda_c^-K0 decays
We report first measurements of the doubly charmed baryonic B decays
B->Lambda_c+Lambda_c-K. The B+->Lambda_c+Lambda_c-K+ decay is observed with a
branching fraction of (6.5+1.0-0.9+-1.1+-3.4)x10^{-4} and a statistical
significance of 15.4sigma. The B0->Lambda_c+Lambda_c-K0 decay is observed with
a branching fraction of (7.9+2.9-2.3+-1.2+-4.2)x10^{-4} and a statistical
significance of 6.6sigma. The branching fraction errors are statistical,
systematic, and the error resulting from the uncertainty of Lambda_c+->pK-pi+
decay branching fraction. The analysis is based on 357fb-1 of data accumulated
at the Y(4S) resonance with the Belle detector at the KEKB asymmetric e+e-
collider.Comment: 10 pages, 3 figure
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
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
An inclusive measurement of the photon energy spectrum in b->s gamma decays
We report a fully inclusive measurement of the flavour changing neutral
current decay b->s gamma in the energy range 1.8 GeV < E* < 2.8 GeV, covering
95% of the total spectrum. Using 140 fb^-1 we obtain BF(b->s gamma)= 3.55 +/-
0.32 +0.30-0.31 +0.11-0.07, where the errors are statistical, systematic and
from theory corrections. We also measure the first and second moments of the
photon energy spectrum above 1.8 GeV and obtain = 2.292 +/- 0.026 +/- 0.034
GeV and -^2 = 0.0305 +/- 0.0074 +/- 0.0063 GeV^2, where the errors are
statistical and systematic.Comment: RevTex4, 6 pages, Submitted to Phys.Rev.Lett. Replaced: added table
of systematic errors. New results take into account radiative J/Psi decay
Measurement of K^+K^- production in two-photon collisions in the resonant-mass region
K^+K^- production in two-photon collisions has been studied using a large
data sample of 67 fb^{-1} accumulated with the Belle detector at the KEKB
asymmetric e^+e^- collider. We have measured the cross section for the process
gamma gamma -> K^+ K^- for center-of-mass energies between 1.4 and 2.4 GeV, and
found three new resonant structures in the energy region between 1.6 and 2.4
GeV. The angular differential cross sections have also been measured.Comment: 24 pages, 8 figures, to appear in Euro. Phys. Jour.
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
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