EPJ

2023 Impact factor 4.2
EPJ C - Particles and Fields
Particles and Fields
Eur. Phys. J. C 5, 379-388
DOI 10.1007/s100529800949

Investigation of CP violation in $\bf{B^0} \rightarrow \bf{J}/\psi \bf{K^0_S}$ decays at LEP

The OPAL Collaboration
K.Ackerstaff8 - et al.

8 CERN, European Organisation for Particle Physics, CH-1211 Geneva 23, Switzerland

Received: 19 March 1998 / Published online: 12 August 1998

Abstract
An investigation of CP violation was performed using a total of 24 candidates for $\mathrm{B^0} \rightarrow \mathrm{J}/\psi \mathrm{K^0_S}$ decay, with a purity of about 60%. These events were selected from 4.4 million hadronic $\rm Z^0$ decays recorded by the OPAL detector at LEP. An analysis procedure, involving techniques to reconstruct the proper decay times and tag the produced b-flavours, $\mathrm{B^0}$ or $\bar{\rm B}^0$, has been developed to allow a first direct study of the time dependent CP asymmetry that, in the Standard Model, is $\sin 2\beta$. The result is

\begin{displaymath} \sin 2\beta = 3.2 _{-2.0}^{+1.8}\ \pm 0.5 \;, \end{displaymath}

where the first error is statistical and the second systematic. This result is used to determine probabilities for different values of $\sin 2\beta$ in the physical region from -1 to +1.

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