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

TL;DR

This paper reports a preliminary measurement of time-dependent CP-violating asymmetries in B0 meson decays to J/psi K0S and psi(2S) K0S, using data from the BABAR detector, with results consistent with previous measurements within uncertainties.

Contribution

First measurement of CP asymmetries in these specific B0 decay channels using neural network tagging at BABAR.

Findings

Measured sin2beta = 0.12 ± 0.37 (stat) ± 0.09 (syst)

Used neural network tagging to improve flavor identification

Analyzed 120 B0 decay candidates

Abstract

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).