We measure the branching fractions of the Ψ(2S) meson to the leptonic final states e+e- and μ+μ- relative to that for Ψ(2S)→J/Ψπ_. The method uses Ψ(2S) mesons produced in the decay of B mesons at the Y(45) resonance in a data sample collected with the BABAR detector at the Stanford Linear Accelerator Center. Using previous measurements for the Ψ(2S) →J/Ψπ+π- branching fraction, we determine the e+e- and π+π- branching fractions to be 0.0078±0.0009±0.0008 and 0.0067±0. 0008±0.0007, respectively. © 2001 The American Physical Society.

The neutral B meson lifetime is measured with the data collected by the BABAR detector at the PEP-II storage ring during the years 1999 and 2000, with a total integrated luminosity of 20.7 fb-1. The decays B0 →D*-π+ and B0→D*-p+ are selected with a partial-reconstruction technique, yielding samples of 6970 ±240 and 5520±250 signal events, respectively. With these events, the B0 lifetime is measured to be 1.533 ±0.034 (stat)±0.038 (syst) ps. This measurement serves as a test and validation of procedures required to measure the CP violation parameter sin(2β+γ) with partial reconstruction of these modes.

New measurements of (Formula presented) and (Formula presented) meson production rates from B decays and from (Formula presented) continuum events near the (Formula presented) resonance are presented. Using 20.8 (Formula presented) of data on the (Formula presented) resonance and 2.6 (Formula presented) off-resonance, we find the inclusive branching fractions (Formula presented) and (Formula presented) where the first error is statistical, the second is systematic, and t he third is due to the (Formula presented) branching fraction uncertainty. The production cross sections (Formula presented) and (Formula presented) are measured at center-of-mass energies about 40 MeV below the (Formula presented) mass. The branching fractions (Formula presented) and (Formula presented) are determined from the (Formula presented) momentum spectra. The mass difference (Formula presented) is also measured. © 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 search for direct CP violation in charmless hadronic B decays observed in a sample of about 22.7 million B B̄ pairs collected with the BABAR detector at the SLAC PEP-II asymmetric-energy e+e- collider. We measure the following charge asymmetries: ACp(B ±→η′K±=-0.11±0. 11±0.02, ACP(B±→ωπ ±) = -0.01 -0.31+0.29±0.03, ACPB±→φK±)= -0.05±0.20±0.03, ACP(B± → φK*±)= -0.430.30+0.36±0.06, and ACP(B0→φ K*0)=0.00±0.27±0.03. © 2002 The American Physical Society.

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.

We present a measurement of the time-dependent CP-violating asymmetries in neutral B decays to the eigenstate, and an updated measurement of the charge asymmetry in B0→K+π-~ decays. In a sample of 33 million Y(4S)→BB̄ decays collected with the BABAR detector at the SLAC PEP-II asymmetric B factory, we find 65-11+12 and 217±18 K+π- candidates and measure the asymmetry parameters Sππ=0.03-0.56+0.53±0.111, Cππ=-0.25-0.17+0.45±0.14, and AKπ = -0.07±0. 08±0.02, where the first error is statistical and the second is systematic. © 2002 The American Physical Society.

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/ ψK S0, ψ(2S)K S0, χ c1K S0, J/ψK* 0 (K* 0→K S0π 0) and J/ψK L0, or in flavor-eigenstate modes involving D (*)π/p/a 1 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 B 0-B̄ 0 oscillation frequency Δm d are measured with a sample of about 6350 fully-reconstructed B 0 decays in hadronic flavor-eigenstate modes. A maximum-likelihood fit to this flavor eigenstate sample finds Δm d=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 B 0 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 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 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 Υ(4S) resonance and 3.9 fb -1 off resonance. One of the neutral B mesons, which are produced in pairs at the Υ(4S), is fully reconstructed in the CP decay modes J/ΨK S 0 , Ψ(2S)K S 0 , X c1 K S 0 , J/ΨK* 0 (K* 0 →K s 0 π 0 ) and J/ΨK L 0 , or in flavor-eigenstate modes involving D(*)π/ρ/a 1 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 network 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 B 0 -B̄ 0 oscillation frequency Δm d are measured with a sample of about 6350 fully-reconstructed B 0 decays in hadronic flavor-eigenstate modes. A maximum-likelihood fit to this flavor eigenstate sample finds Δm d =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 B 0 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.