Measurement of CP Violation in B0 → J/ψ K0S and B0 → ψ(2S) K0S Decays

A measurement is presented of decay-time-dependent CP violation in the decays B0 → J/ψ K0S and B0 → ψ(2S) K0S, where the J/ψ is reconstructed from two electrons and the ψ(2S) from two muons. The analysis uses a sample of pp collision data recorded with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb−1. The CP-violation observables are measured to be C(B0 → J/ψ K0S) = 0.12 ± 0.07 ± 0.02, S(B0 → J/ψ K0S) = 0.83 ± 0.08 ± 0.01, C(B0 → ψ(2S) K0S) = −0.05 ± 0.10 ± 0.01, S(B0 → ψ(2S) K0S) = 0.84 ± 0.10 ± 0.01, where C describes CP violation in the direct decay, and S describes CP violation in the interference between the amplitudes for the direct decay and for the decay after B0 anti-B0 oscillation. The first uncertainties are statistical and the second are systematic. The two sets of results are compatible with the previous LHCb measurement using B0 → J/ψ K0S decays, where the J/ψ meson was reconstructed from two muons. The averages of all three sets of LHCb results are C(B0 → [c anti-c] K0S) = −0.017 ± 0.029, S(B0 → [c anti-c] K0S) = 0.760 ± 0.034, under the assumption that higher-order contributions to the decay amplitudes are negligible. The uncertainties include statistical and systematic contributions.