arXiv subjects

B. Aubert

Publications and source records attributed to B. Aubert.

At least 577 records · Page 32Linked to original sources

arXiv2002

Measurement of the CKM Matrix Element |Vub| with Charmless Exclusive Semileptonic B Meson Decays at BABAR

We present a preliminary measurement of the branching fraction for B to rho e nu and of the CKM matrix element |Vub| using approximately 55 million B Bbar meson pairs collected with the BABAR detector. Using isospin relations for several modes we find BF(B0 to rho- e+ nu) = (3.39+-0.44+-0.52+-0.60)x10^(-4) and |Vub| = (3.69+-0.23+-0.27+0.40-0.59)x10^(-3). The quoted errors are statistical, systematic, and theoretical, respectively. These results are obtained by using five different form-factor calculations.

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arXiv2002

Measurement of the Inclusive Electron Spectrum in Charmless Semileptonic B Decays Near the Kinematic Endpoint

A preliminary result on the study of the inclusive electron spectrum in B -> X_u e nu decays above the kinematic limit for the dominant B -> X_c e nu transitions is presented. This study is performed at the PEP-II asymmetric B Factory, where B meson pairs are produced in the decay of the Upsilon(4S) resonance. For the electron momentum range of 2.3 - 2.6 GeV/c in the Upsilon(4S) rest frame, the partial branching ratio is measured to be Delta B(B -> X_u e nu)=(0.152+-0.014+-0.014) 10^{-3}.

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arXiv2002

Evidence for the Flavor Changing Neutral Current Decays B to K l+ l- and B to K* l+ l-

We present preliminary results from a search for the rare, flavor-changing neutral current decays B to K l+ l- and B to K* l+ l-, where l+ l- is either an e+ e- or mu+ mu- pair. The data sample comprises (84.4 +- 0.9) X 10e6 upsilon(4S) to B B-bar decays (77.8 /fb) collected with the BaBar detector at the PEP-II B factory. For B to K l+ l-, we observe a signal with estimated significance of 4.4 sigma and obtain B(B to K l+ l-) = (0.78 +0.24 -0.20 +0.11 -0.18) X 10e-6 (averaged over l = e and mu). For B to K* l+ l-, we observe an excess of events over background with estimated significance of 2.8 sigma. We obtain B(B to K* l+ l-) = (1.68 +0.68 -0.58 +-0.28) X 10e-6 and the 90% C.L. upper limit B(B to K* l+ l-) < 3.0 X 10e-6.

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arXiv2002

Search for Decays of B0 Mesons into Pairs of Leptons

We present a search for the decays B0->e+e-, B0->mu+mu-, and B0->emu in data collected at the Upsilon(4S) with the BABAR detector at the SLAC B Factory. Using a data set of 54.4 fb-1, we find no evidence for a signal and set the following preliminary upper limits at the 90% confidence level: B(B0->e+e-)< 3.3*10E-7, B(B0->mu+mu-) < 2.0*10E-7, and B(B0->emu) < 2.1*10E-7.

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arXiv2002

Measurement of the First Hadronic Spectral Moment from Semileptonic B Decays

A preliminary determination of the first moment of the hadronic mass distribution <(M_X)^2 - bar{m_D}^2> in semileptonic B decays has been obtained as a function of the minimum lepton momentum, ranging from 0.9 to 1.6 GeV/c. The measurement is based on a new technique involving BBbar events in which one fully reconstructed B meson decays hadronically and the recoiling B decays semileptonically. The mass of the hadrons in the semileptonic decay is determined from a kinematic fit to the whole event. For different minimum lepton momenta, the mass distribution is decomposed into contributions from various charm resonant states and a non-resonant contribution, allowing for the determination of the first moment. From these moments the Heavy Quark Effective Theory (HQET) parameters lambda_1 and Lambdabar can be derived. For lepton momenta in the B rest frame above 1.5 GeV/c, we find a first moment that is compatible with existing measurements. However, if we extend the measurement to lower values of lepton momenta, the data can only be described by Operator Product Expansion calculations if we use significantly different values for Lambdabar and lambda_1 than obtained from earlier measurements based on lepton momentum spectra and the photon spectrum in b --> s gamma transitions.

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arXiv2002

Measurement of the B^0 -> D^-a_1^+ Branching Fraction with Partially Reconstructed D^

The B^0 -> D^*-a_1^+ branching fraction has been measured with data collected by the BABAR experiment in 1999 and 2000 corresponding to a total integrated luminosity of 20.6 fb^-1. Signal events have been selected using a partial reconstruction technique, in which only the a_1^+ and the slow pion (pi_s) from the D^*- decay are identified. A signal yield of 18400 +/- 1200 events has been found, corresponding to a preliminary branching fraction of (1.20 +/- 0.07(stat) +/- 0.14 (syst))%.

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arXiv2002

A Search for the Decay B0 -> pi0 pi0

We present a search for the decay B^0 --> pi^0 pi^0 by the BABAR experiment at the PEP-II asymmetric-energy B-factory at SLAC. Using approximately 88 million B bar{B} pairs collected between 1999 and 2002, we place a 90% confidence level upper limit on the branching fraction of B(B^0 --> pi^0 pi^0) < 3.6 times 10^{-6}. This result is preliminary.

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arXiv2002

Measurements of Branching Fractions and Direct CP Asymmetries in pi^+ pi^0, K^+ pi^0 and K^0 pi^0 B Decays

We present preliminary results of the analyses of B^+ --> h^+ pi^0 (with h^+ = pi^+, K^+) and B^0 --> K^0 pi^0 decays from a sample of approximately 88 million B bar{B} pairs collected by the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We measure the pi^+ pi^0 branching fraction and we obtain B(B^+ --> pi^+ pi^0) = (5.5^{+1.0}_{-0.9} +/- 0.6) times 10^{-6} with a significance of 7.7 sigma including systematic uncertainties. We measure the K^+ pi^0 and K^0 pi^0 branching fractions to be B(B^+ --> K^+ pi^0) = (12.8^{+1.2}_{-1.1} +/- 1.0) times 10^{-6} and B(B^0 --> K^0 pi^0) = (10.4 +/- 1.5 +/- 0.8) times 10^{-6}. At the same time, the direct CP-violating asymmetries are investigated and we find A_{pi^+ pi^0} = -0.03_{-0.17}^{+0.18} +/- 0.02, A_{K^+ pi^0} = -0.09 +/- 0.09 +/- 0.01 and A_{K^0 pi^0} = 0.03 +/- 0.36 +/- 0.09, where the errors are statistical and systematic, respectively.

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arXiv2002

Measurement of the Branching Fraction for B+- --> chi_c0 K+-

We present preliminary results for the measurement of the branching fraction of the decay B+- -> chi_c0 K+- from a sample of 75 million BB pairs collected by the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. The chi_c0 meson is reconstructed through its two-body decays to pi+ pi- and K+ K-. We measure BR(B+- -> chi_c0 K+-) * BR(chi_c0 -> pi+ pi-) = (1.08 +- 0.35 (stat) +- 0.10 (syst))*10^-6 and BR(B+- -> chi_c0 K+-) * BR(chi_c0 -> K+ K-) = (1.48 +- 0.44 (stat) +- 0.17 (syst)) * 10^-6. Using the known values for the chi_c0 decays branching fractions, we combined these results to obtain BR(B+- -> chi_c0 K+-) = (2.4 +- 0.7) * 10^-4.

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arXiv2002

Search for CP Violation in B0/B0b Decays to pi+pi-pi0 and K+-pi-+pi0 in Regions Dominated by the rho+- Resonance

We present preliminary measurements of direct and indirect CP-violating asymmetries in the decays of neutral B mesons to pi+pi-pi0 and K+-pi-+pi0 final states dominated by the rho+- resonance, using a time-dependent maximum likelihood analysis. The data sample comprises 88 10^ Upsilon(4S) -> BBb decays (80.8 fb-1) collected with the BaBar detector at the PEP-II asymmetric-energy B Factory at SLAC. For the CP violation parameters, we measure A_{CP}(rho K) = 0.19 +/- 0.14 (stat) +/- 0.11 (syst), A_{CP}(rho pi) = -0.22 +/- 0.08 (stat) +/- 0.07 (syst), C(rho pi) = 0.45 +0.18/-0.19 (stat) +/- 0.09 (syst), S(rho pi) = 0.16 +/- 0.25 (stat) +/- 0.07 (syst). For the other parameters in the description of the B0B0b -> rho pi decay-time dependence, we obtain DeltaC(rho pi) = 0.38 +0.19/-0.20 (stat) +/- 0.11 (syst), DeltaS(rho pi) = 0.15 +/- 0.26 (stat) +/- 0.05 (syst).

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arXiv2002

A Search for B->Knunubar

We present a preliminary search for the flavor-changing neutral current decay B^+ -> K^+ nunubar using 56 million Y(4S) decays recorded with the BABAR detector at the SLAC B factory. Identification of the B^+ -> K^+ nunubar final state, with two neutrinos, requires the reconstruction of the companion B in the event. The companion B is reconstructed in the decay mode B^- -> D^0 l^- nubar X, which provides both high efficiency and good purity. The particles not used in the reconstruction of the companion B are compared with the signature expected for B^+ -> K^+ nunubar decays. Two candidates are found in the data with an expected background of 2.2 events. Under the assumption that all candidates are signal events, an upper limit on the branching fraction for B^+ -> K^+ nunubar of 9.4 x 10^-5 at 90% confidence level is determined.

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arXiv2002

Measurement of sin2beta in B0 to Phi K0S

We present a preliminary measurement of the time-dependent CP-violating asymmetry in the neutral B decay B0 --> phi K0S, with phi --> K+K- and K0S --> pi+pi-. The measurement uses a data sample of about 87 million Y(4S) --> B Bbar decays collected between 1999 and 2002 with the BaBar detector at the PEP-II asymmetric-energy B Factory at SLAC. In this sample we study events in which the CP final state is fully reconstructed and the flavor of the other neutral B meson is determined from its decay products. The amplitude of the CP-violating asymmetry sin2beta is derived from the decay-time distributions. We measure sin2beta = -0.19 +0.52-0.50 (stat) +/- 0.09 (syst) (preliminary).

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arXiv2002

Simultaneous Measurement of the B0 Meson Lifetime and Mixing Frequency with B0 --> D*- l+ nu_l Decays

We measure the B0 lifetime tau_B0 and the B-Bbar oscillation frequency Deltam_d with a sample of approximately 14,000 exclusively reconstructed B0 -> D*- l+ nu_l signal events, selected from 23 million B-Bbar pairs recorded at the Upsilon(4S) resonance with the BABAR detector at the Stanford Linear Accelerator Center. The b-quark flavor of the other B at the time of decay and its decay position are determined inclusively. The lifetime and oscillation frequency are measured simultaneously with an unbinned maximum-likelihood fit that uses, for each event, the measured difference in B decay times (Delta-t), the calculated uncertainty on Delta-t, the signal and background probabilities, and b-quark tagging information for the other B. The preliminary results are tau_B0 = (1.523 +0.024 -0.023 (stat) +/- 0.022 (syst)) ps and Deltam_d = (0.492 +/- 0.018 (stat) +/- 0.013 (syst)) ps^-1. The statistical correlation coefficient between tau_B0 and Deltam_d is -0.22.

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arXiv2002

Measurement of Time-Dependent CP Asymmetries and the CP-odd Fraction in the Decay B^0 --> D^{+}D^{-}

We present a measurement of time-dependent CP asymmetries and an updated determination of the CP-odd fraction in the decay B^0 --> D^{*+}D^{*-}. The measurements are derived from a data sample of 88 times 10^{6} B bar{B} pairs collected by the BaBar detector at the PEP-II energy asymmetric B Factory at SLAC. All results are preliminary.

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arXiv2002

Search for the Exclusive Radiative Decays B -> rho gamma and B -> omega gamma

A search for the exclusive radiative decays B->rho(770) gamma and B^0->omega(782) gamma is performed on a sample of 84 million BB-bar events collected by the BABAR detector at the PEP-II asymmetric e^+e^- collider. No significant signal is seen in any of the channels. We set preliminary upper limits of BR[B^0->rho^0 gamma]< 1.4 times 10^{-6}, BR[B^+ -> rho^+ gamma] < 2.3 times 10^{-6} and BR[B^0 -> omega gamma]< 1.2 times 10^{-6} at 90% Confidence Level. Combining these into a single limit on the generic process B-> rho gamma, we find the preliminary limit BR[B -> rho gamma]<1.9 times 10^{-6}, corresponding to a limit of BR[B -> rho gamma]/BR[B-> K* gamma] < 0.047 at 90% Confidence Level.

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arXiv2002

b --> s gamma using a Sum of Exclusive Modes

This paper describes preliminary results on the inclusive process b --> s gamma obtained from 20.7 fb^-1 of data recorded with the BaBar detector during 1999-2000. Signal event yields are found from a combination of twelve exclusive decay channels after subtracting continuum and BBbar backgrounds. Cross-feed from incorrectly reconstructed b --> s gamma events is also removed. Branching fractions in bins of hadronic mass are calculated using corrected Monte Carlo signal efficiencies; this is equivalent to measuring the gamma energy spectrum. We measure the first moment of the gamma energy spectrum constraining the HQET parameter LambdaBar = (0.37 +/- 0.09 (stat) +/- 0.07 (syst) +/- 0.10 (model)) GeV/c^2. A fit to the hadronic mass spectrum gives B(b --> s gamma) = (4.3 +/- 0.5 (stat) +/- 0.8 (syst) +/- 1.3 (model))x 10^-4 for the inclusive branching fraction. We also constrain the HQET parameter lambda_1.

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arXiv2002

A Study of The Rare Decays B0 -> Ds()+ pi- and B0 -> Ds()-K+

We report on the evidence for the decays B0 -> Ds+ pi- and B0 -> Ds- K+ and the results of a search for the decays B0 -> Ds*+ pi- and B0 -> Ds*-K+ from a sample of 84 million Upsilon(4S) decays into B meson pairs collected with the BABAR detector at the PEP II asymmetric-energy e^{+}e^{-} collider. The measured B0 -> Ds+ pi- yield has a probability of less than 10^{-3} to be a fluctuation of the background and we measure the branching fraction Br(B0 -> Ds+ pi-) = (3.2 +- 0.9 (stat) +- 1.0 (syst)) x 10^-5. The measured B0 -> Ds- K+ yield has a probability of less than 5 times 10^{-4} to be a fluctuation of the background and we measure the branching fraction Br(B0 -> Ds- K+) = (3.2 +- 1.0 (stat) +- 1.0 (syst)) x 10^-5. We also set 90% C.L. limits Br(B0 -> Ds*+ pi-)< 4.1 x 10^-5 and Br(B0 -> Ds*- K+) < 2.5 x 10^-5. All results are preliminary

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arXiv2002

Measurements of Charmless Two-Body Charged B Decays with Neutral Pions and Kaons

We present preliminary results of the analyses of B into h pi0 and B into hK0 decays (with h = pi+/-, K+/-) from a sample of approximately 60 million BB pairs collected by the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We find evidence for a signal in B+ into pi+ pi0, and we measure the branching fraction BR (B+ into pi+ pi0) = (4.1_{-1.0}^{+1.1}\pm 0.8) 10^{-6}. We also measure the following branching ratios and charge asymmetries: BR(B+ to K+ pi0) = (11.1_{-1.2}^{+1.3} \pm 1.0) 10^{-6}, BR(B+ to pi+ K0) = (17.5^{+1.8}_{-1.7} \pm 1.3)10^{-6}$, BR(B+ to K+ K0bar) < 1.3 10^{-6} (90%$ CL), acp_{pi+ pi0} = -0.02^{+0.27}_{-0.26} \pm 0.10, acp_{K+ pi0} = 0.00\pm 0.11 \pm 0.02$, acp_{pi+ K0} =-0.17\pm 0.10 \pm 0.02, where the errors are statistical and systematic, respectively.

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