Study of the CP asymmetry of B-0 -> J/psi K-S(0) decays in ALEPH

The decay B-0 --> J/psi K-S(0) is reconstructed with J/psi --> e(+)e(-) or mu (+)mu (-) and K-S(0) --> pi (+)pi (-). From the full ALEPH dataset at LEP1 of about 4 million hadronic Z decays, 23 candidates are selected with an estimated purity of 71%, They are used to measure the CP asymmetry of this decay, given by sin 2 beta in the Standard Model, with the result sin 2 beta = 0.84(-1.04)(+0.82) +/- 0.16. This is combined with existing measurements from other experiments, and increases the confidence level that CP violation has been observed in this channel to 98%. (C) 2000 Elsevier Science B.V. All rights reserved.