Study of the CP asymmetry of B0 -> J/psi K0S decays in ALEPH

TL;DR

This paper measures the CP asymmetry in B0 -> J/psi K0_S decays using ALEPH data, providing evidence for CP violation with a combined confidence level of 98%.

Contribution

First measurement of CP asymmetry in B0 -> J/psi K0_S decays using ALEPH data, supporting CP violation observation.

Findings

Measured sin 2beta = 0.84 +0.82-1.04 +-0.16

Combined with other experiments, confidence level for CP violation is 98%

Supports the Standard Model prediction of CP violation in B decays.

Abstract

The decay B0 -> J/psi K0_S is reconstructed with J/psi -> e+ e- or mu+ mu- and K0_S -> 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 2beta in the Standard Model, with the result sin 2beta = 0.84 +0.82-1.04 +-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%.