arXiv subjects

B. Aubert

Publications and source records attributed to B. Aubert.

At least 631 records · Page 35Linked to original sources

arXiv2001

Measurement of the B^0 and B^+ meson lifetimes with fully reconstructed hadronic final states

The B0 and B+ meson lifetimes have been measured in e+e- annihilation data collected in 1999 and 2000 with the BABAR detector at center-of-mass energies near the Upsilon(4S) resonance. Events are selected in which one B meson is fully reconstructed in a hadronic final state while the second B meson is reconstructed inclusively. A combined fit to the B0 and the B+ decay time difference distributions yields tau_{B0} = 1.546 +/- 0.032 (stat) +/- 0.022(syst) ps, tau_{B+} = 1.673 +/- 0.032 (stat) +/- 0.023 (syst) ps and tau_{B+} / tau_{B0} = 1.082 +/- 0.026 (stat) +/- 0.012 (syst).

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arXiv2001

Observation of CP violation in the B^0 meson system

We present an updated measurement of time-dependent CP-violating asymmetries in neutral B decays with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. This result uses an additional sample of Upsilon(4S) decays collected in 2001, bringing the data available to 32 million B-anti-B pairs. We select events in which one neutral B meson is fully reconstructed in a final state containing charmonium and the flavor of the other neutral B meson is determined from its decay products. The amplitude of the CP-violating asymmetry, which in the Standard Model is proportional to sin2beta, is derived from the decay time distributions in such events. The result sin2beta = 0.59 +/- 0.14 (stat) +/- 0.05 (syst) establishes CP violation in the B^0 meson system. We also determine |lambda| = 0.93 +/- 0.09 {stat} +/- 0.03 {syst}, consistent with no direct CP violation.

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arXiv2001

Measurement of Branching Fractions and Search for CP-Violating Charge Asymmetries in Charmless Two-Body B Decays into Pions and Kaons

We present measurements of the branching fractions and a search for CP-violating charge asymmetries in charmless hadronic decays of B mesons into two-body final states of kaons and pions. The results are based on a data sample of approximately 23 million BB(bar) pairs collected by the BABAR detector at the PEP-II asymmetric B Factory at SLAC. We find the following branching fractions: BF(B0-->pi+pi-)= (4.1+/-1.0+/-0.7) x 10^{-6}, BF(B0-->K+pi-)=(16.7+/-1.6+/-1.3) x 10^{-6}, BF(B+-->K+pi0)=(10.8^{+2.1}_{-1.9}+/-1.0) x 10^{-6}, BF(B+-->K0pi+)=(18.2^{+3.3}_{-3.0}+/-2.0) x 10^{-6}, BF(B0-->K0pi0)=(8.2^{+3.1}_{-2.7}+/-1.2) x 10^{-6}. We also report the 90% confidence level upper limits BF(B0-->K+K-) < 2.5 x 10^{-6}, BF(B+-->pi+pi0) < 9.6 x 10^{-6}, and BF(B+-->anti-K0K+) < 2.4 x 10^{-6}. In addition, charge asymmetries have been measured and found to be consistent with zero, where the statistical precision is in the range of +/-0.10 to +/-0.18, depending on the decay mode.

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arXiv2001

Measurement of the decays B-->phi K and B-->phi K^*

We have observed the decays B-->phi K and phi K^* in a sample of over 45 million B mesons collected with the BABAR detector at the PEP-II collider. The measured branching fractions are BF(B^+ --> phi K^+) = (7.7^{+1.6}_{-1.4}+/- 0.8) x 10^{-6}, BF(B^0 --> phi K^0) = (8.1^{+3.1}_{-2.5}+/- 0.8) x 10^{-6}, BF(B^+ --> phi K^{*+}) = (9.7^{+4.2}_{-3.4}+/- 1.7) x 10^{-6}, and BF(B^0 --> phi K^{*0}) = (8.6^{+2.8}_{-2.4}+/- 1.1) x 10^{-6}. We also report the upper limit BF(B^+ --> phi pi^+) < 1.4 x 10^{-6}$ (90% CL).

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arXiv2001

Measurement of CP-violating asymmetries in B0 decays to CP eigenstates

We present measurements of time-dependent CP-violating asymmetries in neutral B decays to several CP eigenstates. The measurement uses a data sample of 23 million Upsilon(4S)-->B-anti-B decays collected by the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we find events where one neutral B meson is fully reconstructed in a CP eigenstate containing charmonium and the flavor of the other neutral B meson is determined from its decay products. The amplitude of the CP-violating asymmetry, which in the Standard Model is proportional to sin2beta, is derived from the decay time distributions in such events. The result is sin2beta=0.34 +/- 0.20 (stat) +/- 0.05 (syst).

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arXiv2000

The first year of the BABAR experiment at PEP-II

The BABAR detector, situated at the SLAC PEP-II asymmetric e^+e^- collider, has been recording data at energies on and around the Upsilon(4S) resonance since May 1999. In this paper, we briefly describe the PEP-II B Factory and the BABAR detector. The performance presently achieved by the experiment in the areas of tracking, vertexing, calorimetry and particle identification is reviewed. Analysis concepts that are used in the various papers submitted to this conference are also discussed.

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arXiv2000

A measurement of the charged and neutral B meson lifetimes using fully reconstructed decays

Data collected with the BABAR detector at the PEP-II asymmetric B Factory at SLAC are used to study the lifetimes of the B^0 and B^+ mesons. The data sample consists of 7.4 fb-1 collected near the Y(4S) resonance. B^0 and B^+ mesons are fully reconstructed in several exclusive hadronic decay modes to charm and charmonium final states. The B lifetimes are determined from the flight length difference between the two B mesons which are pair-produced in the Y(4S) decay. The preliminary measurements of the lifetimes are tau_B0 = 1.506+/-0.052(stat)+/-0.029(syst) ps, tau_B+ = 1.602+/-0.049(stat)+/-0.035(syst) ps, and of their ratio is tau_B+/tau_B0 = 1.065+/-0.044(stat)+/-0.021(syst).

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arXiv2000

A study of time-dependent CP-violating asymmetries in B0 -> J/psi K0S and B0 -> psi(2S) K0S decays

We present a preliminary measurement of time-dependent CP-violating asymmetries in B0 -> J/psi K0S and B0 -> psi(2S) K0S decays recorded by the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. The data sample consists of 9.0 fb-1 collected at the Y(4S) resonance and 0.8 fb-1 off-resonance. One of the neutral B mesons, produced in pairs at the Y(4S), is fully reconstructed. The flavor of the other neutral B meson is tagged at the time of its decay, mainly with the charge of identified leptons and kaons. A neural network tagging algorithm is used to recover events without a clear lepton or kaon tag. The time difference between the decays is determined by measuring the distance between the decay vertices. Wrong-tag probabilities and the time resolution function are measured with samples of fully-reconstructed semileptonic and hadronic neutral B final states. The value of the asymmetry amplitude, sin2beta, is determined from a maximum likelihood fit to the time distribution of 120 tagged B0 -> J/psi K0S and B0 -> psi(2S) K0S candidates to be sin2beta = 0.12+/-0.37 (stat) +/- 0.09 (syst) (preliminary).

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arXiv2000

Measurement of inclusive production of charmonium states in B meson decays

We reconstruct the charmonium mesons J/psi, psi(2S) and chi_C1 using a sample of 8.46 x 10^6 B-anti-B events collected by the BABAR detector operating at e^+e^- center of mass energies near the Y(4S) resonance. By measuring rates relative to the branching fraction of the J/psi, we obtain preliminary inclusive B branching fractions of (0.25+/-0.02+/-0.02)% to the psi(2S) and (0.39+/-0.04+/-0.04)% to the chi_C1, and set a 90% confidence level limit of 0.24% on decays through the chi_C2.

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arXiv2000

Exclusive B decays to charmonium final states

We report on exclusive decays of B mesons into final states containing charmonium using data collected with the BABAR detector at the PEP-II storage rings. The charmonium states considered here are J/psi, psi(2S), and chi_C1. Branching fractions for several exclusive final states, a measurement of the decay amplitudes for the B0 --> J/psi K* decay, and measurements of the B0 and B+ masses are presented. All of the results we present here are preliminary.

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arXiv2000

Measurement of the branching fractions for B^0 -> D^{-}pi^+ and B^0 -> D^{-}rho^+

Using 5.2 fb-1 of e^+e^- annihilation data recorded with the BABAR detector at the PEP-II storage ring while operating on the Y(4S) resonance, a sample of fully reconstructed B^0 decays in the hadronic modes B^0 -> D^{*-}pi^+ and B^0 -> D^{*-}rho^+ have been reconstructed. In this paper, a study of these events is reported, including preliminary measurements of the absolute branching fractions for these modes, which are found to be B(B^0 -> D^{*-}pi^+) = (2.9+/-0.3+/-0.3) x 10^{-3} and B(B^0 -> D^{*-}rho^+) = (11.2+/-1.1+/-2.5) x 10^{-3}.

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arXiv2000

A measurement of the B^0-anti-B^0 oscillation frequency and determination of flavor-tagging efficiency using semileptonic and hadronic B^0 decays

B^0-anti-B^0 flavor oscillations are studied in e^+e^- annihilation data collected with the BABAR detector at center-of-mass energies near the Y(4S) resonance. One B is reconstructed in a hadronic or semileptonic decay mode, and the flavor of the other B in the event is determined with a tagging algorithm that exploits the relation between the flavor of the heavy quark and the charges of its decay products. Tagging performance is characterized by an efficiency e_i and a probability for mis-identification, w_i, for each tagging category. We report a determination of the wrong-tag probabilities, w_i, and a preliminary result for the time-dependent B^0-anti-B^0 oscillation frequency, Delta_md = 0.512+/-0.017+/-0.022 hbar-ps^{-1}.

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arXiv2000

Measurement of the B^0 meson properties using partially reconstructed B^0 to D^{-}pi^+ and B^0 to D^{-}l^+nu decays with the BABAR detector

The two B^0 decay processes B^0 --> D^{*-}pi^+ and B^0 --> D^{*-}l^+nu have been studied by means of a partial reconstruction technique using a data sample collected with the BABAR detector at the PEP-II storage ring. To increase statistics, only the soft pi^- from the decay D^{*-} --> pi^-D^0 was used in association with either an oppositely-charged high-momentum pion or lepton. Events were then identified by exploiting the constraints from the simple kinematics of Y(4S) decays. A clear signature is obtained in each case. The position of the B^0 decay point was obtained from the reconstructed pi^+(l^+)pi^- vertex. The position of the other anti-B^0 in the event was also determined. Taking advantage of the boost given to the Y(4S) system by the asymmetric beam energies of PEP-II, the lifetime of the B^0 meson has been measured from the separation distance between the two vertices along the beam direction. The preliminary results are tau_B0 = 1.55+/-0.05+/-0.07 ps, tau_B0 = 1.62+/-0.02+/-0.09 ps, respectively for the B^0 --> D^{*-}pi^+ and B^0 --> D^{*-}l^+nu channels.

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arXiv2000

Measurement of the time dependence of B^0-anti-B^0 oscillations using inclusive dilepton events

A preliminary study of time dependence of B^0-anti-B^0 oscillations using dilepton events is presented. The flavor of the B meson is determined by the charge sign of the lepton. To separate signal leptons from cascade and fake leptons we have used a method which combines several discriminating variables in a neural network. The time evolution of the oscillations is studied by reconstructing the time difference between the decays of the B mesons produced by the Y(4S) decay. With an integrated luminosity of 7.7 fb-1 collected on resonance by BABAR at the PEP-II asymmetric B Factory, we measure the difference in mass of the neutral B eigenstates, Delta_mB0, to be (0.507+/-0.015+/-0.022) x 10^{12} hbar-s^{-1}.

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arXiv2000

A measurement of the branching fraction of the exclusive decay B^0 --> K^{*0}gamma

The b --> s gamma transition proceeds by a loop ``penguin'' diagram. It may be used to measure precisely the couplings of the top quark and to search for the effects of any new particles appearing in the loop. We present a preliminary measurement of the branching fraction of the exclusive decay, B^0 --> K^{*0}gamma. We use 8.6 x 10^6 B-anti-B decays to measure B(B^0 --> K^{*0}gamma) = (5.4+/-0.8+/-0.5) x 10^{-5}.

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arXiv2000

Study of inclusive D_S^(()+/-) production in B decays and measurement of B^0 --> D^(-)D_S^((*)+) decays using a partial reconstruction technique

Electron-positron annihilation data collected by the BABAR detector near the Y(4S) resonance are used to study the inclusive decay of B mesons to D_S^(+/-) and D_S^(*+/-) mesons, where the D_S^(+/-) is reconstructed using the decay D_S^(+/-) --> phi pi^(+/-). The production fraction of inclusive D_S^((*)+/-) and the corresponding momentum spectra have been determined. The exclusive decays B^0 --> D^(*-)D_S^((*)+) are observed with a partial reconstruction technique which uses the soft pion from the D^(*+/-) decay in association with the reconstructed D_S^((*)+/-). The beam energy constraint is used to determine the missing mass recoiling against the D_S^(+/-) system, showing a clear signal for this process. From the observed rates, preliminary results for the corresponding branching fractions have been obtained.

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arXiv2000

Measurement of branching fractions for two-body charmless B decays to charged pions and kaons at BABAR

We present preliminary results of a search for charmless two-body B decays to charged pions and kaons using data collected by the BABAR detector at the Stanford Linear Accelerator Center's PEP-II storage ring. In a sample of 8.8 million produced B-anti-B pairs we measure the branching fractions B(B^0 --> pi^+pi^-) = (9.3^{+2.6}_{-2.3}^{+1.2}_{-1.4}) x 10^{-6} and B(B^0 --> K^+π^-) = (12.5^{+3.0}_{-2.6}^{+1.3}_{-1.7}) x 10^{-6}, where the first uncertainty is statistical and the second is systematic. For the decay B^0 --> K^+K^- we find no significant signal and set an upper limit of B(B^0 --> K^+K^-) < 6.6 x 10^{-6} at the 90% confidence level.

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arXiv2000

Measurements of charmless three-body and quasi-two-body B decays

We present preliminary results of a search for several exclusive charmless hadronic B decays from electron-positron annihilation data collected by the BABAR detector near the Y(4S) resonance. These include three-body decay modes with final states h^{+/-}h^{-/+}h^{+/-} and h^{+/-}h^{-/+}pi^0, and quasi-two-body decay modes with final states X^0 h and X^0 K0S, where h = pi or K and X^0 = eta^' or omega. We find B(B^0 --> rho^(-/+)pi^(+/-)) = (49+/-13^{+6}_{-5}) x 10^{-6} and B(B^+ --> eta^' K^+) = (62+/-18+/-8) x 10^{-6} and present upper limits for eight other decays.

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