We present a measurement of time-dependent CP-violating asymmetries in neutral B meson decays collected with the BABAR detector at the PEP-II asymmetric-energy e+e- collider at the Stanford Linear Accelerator Center. The data sample consists of 29.7 fb-1 recorded at the γ(4S) resonance and 3.9 fb-1 off resonance. One of the neutral B mesons, which are produced in pairs at the γ(4S), is fully reconstructed in the CP decay modes J/ ψKS0, ψ(2S)KS0, χc1KS0, J/ψK*0 (K*0→KS0π0) and J/ψKL0, or in flavor-eigenstate modes involving D(*)π/p/a1 and J/ψK*0 (K*0→K+π -). 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 netsvork tagging algorithm is used to recover events without a clear lepton or kaon tag. The proper time elapsed between the decays is determined by measuring the distance between the decay vertices. Wrong-tag probabilities, the time-difference resolution function, and the B0-B̄0 oscillation frequency Δmd are measured with a sample of about 6350 fully-reconstructed B0 decays in hadronic flavor-eigenstate modes. A maximum-likelihood fit to this flavor eigenstate sample finds Δmd=0.516±0.016(stat)±0.010(syst) ps -1. The value of the asymmetry amplitude sin 2β is determined from a simultaneous maximum-likelihood fit to the time-difference distribution of the flavor-eigenstate sample and about 642 tagged B0 decays in the CP-eigenstate modes. We find sin 2β=0.59 ±0.14(stat)±0. 05(syst), demonstrating that CP violation exists in the neutral B meson system. We also determine the value of the CP violation parameter |λ|=0. 93±0.09(stat)±0.03(syst), which is consistent with the expectation of |λ|=1 for no direct CP violation. © 2002 The American Physical Society.

We have studied the B±→J/ψπ± and B±→J/ψK± decays using a 20.7 fb-1 data set collected with the BABAR detector. We observe a signal of 51±10 B±→J/ψπ± events and determine the ratio B(B± →J/ψπ±)/B(B±→J/ψ K±) to be [3.91±0.78(stat)±0.19(syst)]%. The CP-violating charge asymmetries for the B±→J/ψπ± and B±→J/ψK± decays are determined to be Aπ=0.01±0.22(stat)±0.01(syst) and AK =0.003±0.030(stat)±0.004(syst).

We present measurements of branching fractions and CP-violating asymmetries for neutral B meson decays to two-body final states of charged pions and kaons based on a sample of about 88 million Y(4S)-->BB decays. From a time-independent fit we measure the charge-averaged branching fractions B(B0-->pi+pi-) = (4.7 +/- 0.6 +/- 0.2) x 10^-6, B(B0-->K+pi-) = (17.9 +/- 0.9 +/- 0.7) x 10^-6, and the direct CP-violating charge asymmetry A(Kpi) = -0.102 +/- 0.050 +/- 0.016; [-0.188,-0.016], where the ranges in square brackets indicate the 90% confidence intervals. From a time-dependent fit we measure the B0-->pi+pi- CP-violating parameters Spipi = 0.02 +/- 0.34 +/- 0.05; [-0.54,+0.58] and Cpipi = -0.30 +/- 0.25 +/- 0.04; [-0.72,+0.12].

New measurements of Ds+ and Ds*+ meson production rates from B decays and from qq̄ continuum events near the Y(4S) resonance are presented. Using 20.8 fb-1 of data on the Y(4S) resonance and 2.6 fb-1 off-resonance, we find the inclusive branching fractions B(B→Ds+ X)=(10.93±0.19±0.58±2.73)% and B(B→Ds*+X)=(7.9±0.8±0.7 ±2.0)%, where the first error is statistical, the second is systematic, and the third is due to the Ds+→φπ+ branching fraction uncertainty. The production cross sections σ(e+e- →Ds+X) × B(Ds+→φπ+)=7.55±0.20 ±0.34 pb and σ(e+e-→Ds *±X) × B(Ds+→φπ+) = 5.8±0.7±0.5 pb are measured at center-of-mass energies about 40 MeV below the Y(4S) mass. The branching fractions ΣB(B→Ds(*)+ D̄(*))=(5.07±0.14±0.30±1.27)% and ∑B(B→Ds*+D̄(*)) =(4.1±0.2±0.4±1.0)% are determined from the Ds(*)+ momentum spectra. The mass difference m(Ds+)-m(D+)=98.4±0.1 ±0.3 MeV/c2 is also measured.

Measurement of time-dependent conjugation (C) and parity (P) asymmetries and the CP-odd fraction in the decay B0→D*+D *- was discussed. It was found that this measurement of R⊥ supersedesthe BABAR results with a factor of 3 reduction in statistical uncertainty. Results also showed that B0→D*+D*- is mostly CP even.

We measure the B0 lifetime τB0 and the B 0-B̄0 oscillation frequency Δmd with a sample of approximately 14000 exclusively reconstructed B 0→D*-ℓ+vℓ signal events, selected from 23 million BB̄ pairs recorded at the Y(45) resonance with the BABAR detector at the Stanford Linear Accelerator Center. The decay position of the other B is determined with the remaining tracks in the event, and its b-quark flavor at the time of decay is determined with a tagging algorithm that exploits the correlation between the flavor of the b quark and the charges of its decay products. The lifetime and oscillation frequencies are measured simultaneously with an unbinned maximum-likelihood fit that uses, for each event, the measured difference in decay times of the two B mesons (Δt), the calculated uncertainty on Δt, the signal and background probabilities, and b-quark tagging information for the other B. The results are τB0=(1.523-0.023+0.024±0.022) ps and Δmd=(0.492±0.018 ±0.013) ps-1. The statistical correlation coefficient between τB0 and Δm d is -0.22. © 2003 The American Physical Society.

We present a study of the decay B--->D(*0)K(*-) based on a sample of 86 x 10(6) Upsilon(4S)-->BBmacr; decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We measure the branching fraction B(B--->D(*0)K(*-))=(8.3+/-1.1(stat)+/-1.0(syst)) x 10(-4), and the fraction of longitudinal polarization in this decay to be Gamma(L)/Gamma=0.86+/-0.06(stat)+/-0.03(syst).