First CP Violation Results from BABAR

TL;DR

This paper reports the first measurement of time-dependent CP violation in B^0 decays using data from the BABAR detector, providing a preliminary value for sin(2*beta) with associated uncertainties.

Contribution

It presents the initial measurement of sin(2*beta) in B^0 decays at BABAR, demonstrating the experimental approach and analysis techniques for CP violation.

Findings

Measured sin(2*beta) = 0.12 ± 0.37 (stat) ± 0.09 (syst)

Analyzed 120 B^0 decay candidates for CP asymmetry

Developed methods for flavor tagging and decay time measurement

Abstract

We present a preliminary measurement of time-dependent CP-violating asymmetries in B^0-->J/psi K_S and B^0-->psi(2S) K_S decays recorded by the BABAR detector at the PEP-II asymmetric B Factory at SLAC. The data sample consists of 9.0 fb-1 collected at the Upsilon(4S) resonance and 0.8 fb-1 off-resonance. One of the neutral B mesons, produced in pairs at the Upsilon(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. 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, sin(2*beta), is determined from a maximum likelihood fit to the time distribution of 120 tagged B^0-->J/psi K_S and B^0-->psi(2S) K_S candidates: sin(2*beta) = 0.12+/-0.37(stat)+/-0.09(syst).