Study of time-dependent CP-violating asymmetries and flavor oscillations in neutral B decays at the Υ(4S) -: art. no. 032003

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 Y(4S) resonance and 3.9 fb-1 off resonance. One of the neutral B mesons, which are produced in pairs at the Y(4S), is fully reconstructed in the CP decay modes J/psiK(S)(0), psi(2S)K-S(0), chi(c1)K(S)(0), J/psiK(*0) (K-*0-->K(S)(0)pi(0)) and J/psiK(L)(0), or in flavor-eigenstate modes involving D((*))pi/rho/a(1) and J/psiK(*0) (K-*0-->K(+)pi(-)). 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-(B) over bar (0) oscillation frequency Deltam(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 Deltam(d)=0.516+/-0.016(stat)+/-0.010(syst) ps(-1). The value of the asymmetry amplitude sin 2beta 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 2beta=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 \lambda\=0.93+/-0.09(stat)+/-0.03(syst), which is consistent with the expectation of \lambda\=1 for no direct CP violation.