101 research outputs found
Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events
The - oscillation frequency has been measured with a sample of
23 million \B\bar B pairs collected with the BABAR detector at the PEP-II
asymmetric B Factory at SLAC. In this sample, we select events in which both B
mesons decay semileptonically and use the charge of the leptons to identify the
flavor of each B meson. A simultaneous fit to the decay time difference
distributions for opposite- and same-sign dilepton events gives ps.Comment: 7 pages, 1 figure, submitted to Physical Review Letter
Observation of B0→χc0K*0 and evidence for B+→χc0K*+
We present the observation of the decay B 0 → χ c 0 K * 0 as well as evidence of B + → χ c 0 K * + , with an 8.9 and a 3.6 standard deviation significance, respectively, using a data sample of 454 × 10 6 Υ ( 4 S ) → B ¯¯¯ B decays collected with the BABAR detector at the PEP-II B meson factory located at the Stanford Linear Accelerator Center (SLAC). The measured branching fractions are B ( B 0 → χ c 0 K * 0 ) = ( 1.7 ± 0.3 ± 0.2 ) × 10 − 4 and B ( B + → χ c 0 K * + ) = ( 1.4 ± 0.5 ± 0.2 ) × 10 − 4 , where the first quoted errors are statistical and the second are systematic. We obtain a branching fraction upper limit of B ( B + → χ c 0 K * + ) < 2.1 × 10 − 4 at the 90% confidence level
Study of Bbar --> Xu l nubar decays in BBbar events tagged by a fully reconstructed B-meson decay and determination of |V_{ub}|
We report measurements of partial branching fractions for inclusive charmless
semileptonic B decays Bbar --> Xu l nubar, and the determination of the CKM
matrix element |V_{ub}|. The analysis is based on a sample of 467 million
Upsilon(4S) --> BBar decays recorded with the BaBar detector at the PEP-II e^+
e^- storage rings. We select events in which the decay of one of the B mesons
is fully reconstructed and an electron or a muon signals the semileptonic decay
of the other B meson. We measure partial branching fractions DeltaB in several
restricted regions of phase space and determine the CKM element |V_{ub}| based
on four different QCD predictions. For decays with a charged lepton momentum
p_l^* > 1.0 GeV in the B meson rest frame, we obtain DeltaB = (1.80 \pm 0.13
(stat.) \pm 0.15 (sys.) \pm 0.02 (theo.)) \times 10^{-3} from a fit to the
two-dimensional mX-q^2 distribution. Here, mX refers to the invariant mass of
the final state hadron X and q^2 is the invariant mass squared of the charged
lepton and neutrino. From this measurement we extract |V_{ub}| = (4.33\pm 0.24
(exp.) \pm 0.15 (theo.)) \times 10^{-3} as the arithmetic average of four
results obtained from four different QCD predictions of the partial rate. We
separately determine partial branching fractions for B^0 and B^- decays and
derive a limit on the isospin breaking in Bbar --> Xu l nubar decays.Comment: 26 pages, 9 postscript figures, 9 tables, accepted for publication in
PR
Measurement of the electron energy spectrum and its moments in inclusive B -> Xe nu decays
We report a measurement of the inclusive electron energy spectrum for semileptonic decays of B mesons in a data sample of 52 million Y(4S)-->B(B) over bar decays collected with the BABAR detector at the PEP-II asymmetric-energy B-meson factory at SLAC. We determine the branching fraction, first, second, and third moments of the spectrum for lower cutoffs on the electron energy between 0.6 and 1.5 GeV. We measure the partial branching fraction to be B(B-->Xenu,E-e>0.6 GeV)=[10.36+/-0.06(stat.)+/-0.23(sys.)]%
Measurement of time-dependent CP asymmetries in B-0 -> D-(*)+/-pi(-/+) decays and constraints on sin(2 beta+gamma)
We present a measurement of CP-violating asymmetries in fully reconstructed B-0-->D((*)+/-)pi(-/+) decays in approximately 88x10(6) Y(4S)-->B (B) over bar decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. From a time-dependent maximum-likelihood fit we obtain the following for the CP-violating parameters: a=-0.022+/-0.038 (stat)+/-0.020 (syst), a(*)=-0.068+/-0.038 (stat)+/-0.020 (syst), c(lep)=+0.025+/-0.068 (stat)+/-0.033 (syst), and c(lep)(*)=+0.031+/-0.070 (stat)+/-0.033 (syst). Using other measurements and theoretical assumptions we interpret the results in terms of the angles of the Cabibbo-Kobayashi-Maskawa unitarity triangle, and find parallel tosin(2beta+gamma)parallel to>0.69 at 68% confidence level. We exclude the hypothesis of no CP violation [sin(2beta+gamma)=0] at 83% confidence level
Measurement of ISR-FSR interference in the processes e+ e- --> mu+ mu- gamma and e+ e- --> pi+ pi- gamma
Charge asymmetry in processes e+ e- --> mu+ mu- gamma and e+ e- --> pi+ pi-
gamma is measured using 232 fb-1 of data collected with the BABAR detector at
center-of-mass energies near 10.58 GeV. An observable is introduced and shown
to be very robust against detector asymmetries while keeping a large
sensitivity to the physical charge asymmetry that results from the interference
between initial and final state radiation. The asymmetry is determined as
afunction of the invariant mass of the final-state tracks from production
threshold to a few GeV/c2. It is compared to the expectation from QED for e+ e-
--> mu+ mu- gamma and from theoretical models for e+ e- --> pi+ pi- gamma. A
clear interference pattern is observed in e+ e- --> pi+ pi- gamma, particularly
in the vicinity of the f_2(1270) resonance. The inferred rate of lowest order
FSR production is consistent with the QED expectation for e+ e- --> mu+ mu-
gamma, and is negligibly small for e+ e- --> pi+ pi- gamma.Comment: 32 pages,29 figures, to be submitted to Phys. Rev.
Measurement of CP Asymmetries and Branching Fractions in Charmless Two-Body B-Meson Decays to Pions and Kaons
We present improved measurements of CP-violation parameters in the decays
, , and , and of
the branching fractions for and . The
results are obtained with the full data set collected at the
resonance by the BABAR experiment at the PEP-II asymmetric-energy factory
at the SLAC National Accelerator Laboratory, corresponding to
million pairs. We find the CP-violation parameter values and
branching fractions where in each case, the first uncertainties are statistical
and the second are systematic. We observe CP violation with a significance of
6.7 standard deviations for and 6.1 standard deviations for
, including systematic uncertainties. Constraints on the
Unitarity Triangle angle are determined from the isospin relations
among the rates and asymmetries. Considering only the solution
preferred by the Standard Model, we find to be in the range
at the 68% confidence level.Comment: 18 pages, 11 postscript figures, submitted to Phys. Rev.
Bottomonium spectroscopy and radiative transitions involving the chi(bJ)(1P, 2P) states at BABAR
We use (121 +/- 1) million Upsilon(3S) and (98 +/- 1) million Upsilon(2S) mesons recorded by the BABAR detector at the PEP-II e(+)e(-) collider at SLAC to perform a study of radiative transitions involving the chi(bJ)(1P, 2P) states in exclusive decays with mu(+)mu(-)gamma gamma final states. We reconstruct twelve channels in four cascades using two complementary methods. In the first we identify both signal photon candidates in the electromagnetic calorimeter (EMC), employ a calorimeter timing-based technique to reduce backgrounds, and determine branching-ratio products and fine mass splittings. These results include the best observational significance yet for the chi(b0)(2P) -> gamma Upsilon(2S) and chi(b0)(1P) -> gamma Upsilon(1S) transitions. In the second method, we identify one photon candidate in the EMC and one which has converted into an e(+)e(-) pair due to interaction with detector material, and we measure absolute product branching fractions. This method is particularly useful for measuring Upsilon(3S) -> gamma chi(b1,2)(1P) decays. Additionally, we provide the most up-to-date derived branching fractions, matrix elements and mass splittings for chi(b) transitions in the bottomonium system. Using a new technique, we also measure the two lowest-order spin-dependent coefficients in the nonrelativistic QCD Hamiltonian
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Observation of the baryonic decay B¯0→Λ+cp¯K−K+
We report the observation of the baryonic decay (B) over bar (0) -> Lambda(+)(c)(p) over barK(-)K(+) using a data sample of 471 x 10(6) B (B) over bar pairs produced in e(+)e(-) annihilations at root s = 10.58 GeV. This data sample was recorded with the BABAR detector at the PEP- II storage ring at SLAC. We find B((B) over bar (0) -> Lambda(+)(c)(p) over barK(-)K(+)) = (2.5 +/- 0.4((stat)) +/- 0.2((syst)) +/- 0.6(B(Lambda c+)) ) x 10(-5) where the uncertainties are statistical, systematic, and due to the uncertainty of the Lambda(+)(c) -> (p) over barK(-)pi(+) branching fraction, respectively. The result has a significance corresponding to 5.0 standard deviations, including all uncertainties. For the resonant decay (B) over bar (0) -> Lambda(+)(c)(p) over bar phi, we determine the upper limit B((B) over bar (0) -> Lambda(+)(c)(p) over bar phi) < 1.2 x 10(-5) at 90% confidence level
Study of the e(+)e(-) -> K+K- reaction in the energy range from 2.6 to 8.0 GeV
The cross section and charged-kaon electromagnetic form
factor are measured in the center-of-mass energy range () from 2.6
to 8.0 GeV using the initial-state radiation technique with an undetected
photon. The study is performed using 469 fb of data collected with the
BABAR detector at the PEP-II collider at center-of-mass energies near
10.6 GeV. The form factor is found to decrease with energy faster than ,
and approaches the asymptotic QCD prediction. Production of the final
state through the and intermediate states is observed. The
results for the kaon form factor are used together with data from other
experiments to perform a model-independent determination of the relative phases
between single-photon and strong amplitudes in and decays. The values of the branching fractions measured in the reaction
are shifted relative to their true values due to
interference between resonant and nonresonant amplitudes. The values of these
shifts are determined to be about for the meson and
for the meson.Comment: 18 pages, 19 postscript figure
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