Measurements are presented of the $CP$ violation observables $S$ and $C$ in the decays of $B^0$ and ${\overline{B}}^0$ mesons to the $J/\psi K_S^0$ final state. The data sample corresponds to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$ collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, and contains a total of 41 560 selected $B^0$ and ${\overline{B}}^0$ decays. The analysis of the time evolution of these decays yields $S=0.731\pm 0.035(\text{stat})\pm 0.020(\text{syst})$ and $C=-0.038\pm 0.032(\text{stat})\pm 0.005(\text{syst})$. In the standard model, $S$ equals $\sin (2\beta )$ to a good level of precision. The values are consistent with the current world averages and with the standard model expectations.

• Received 25 March 2015

DOI:https://doi.org/10.1103/PhysRevLett.115.031601

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© 2015 CERN, for the LHCb Collaboration