Measurements of CP violation in B⁰→[c anti c]K⁰_S transitions at LHCb

This thesis presents a measurement of decay-time-dependent CP violation in the decays B⁰→J/ψ/K⁰_S and B⁰→ψ(2S)K⁰_S, where the J/ψ is reconstructed from two electrons and the ψ(2S) from two muons. The used data sample corresponds to an integrated luminosity of 3 fb^-1 of pp collisions and has been recorded by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The CP violation observables are measured to be C(B⁰→ J/ψK⁰_S)=0.12±0.07(stat.)±0.02(syst.), S(B⁰→J/ψK⁰_S)=0.83±0.08(stat.)±0.01(syst.), C(B⁰→ψ(2S)K⁰_S)=-0.05±0.10(stat.)±0.01(syst.), S(B⁰→ψ(2S)K⁰_S)=0.84±0.10(stat.)±0.01(syst.), 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 results are compatible with the previous LHCb measurement that used B⁰→J/ψK⁰_S decays, where the J/ψ was reconstructed from two muons. A combination of these three measurements results in C(B⁰→[c anti c]K⁰_S)=-0.017±0.029(stat.+syst.),S(B⁰→[c anti c]K⁰_S)=0.760±0.034(stat.+syst.), assuming that higher-order contributions can be neglected. The results are compatible with previous measurements and improve the precision of S at LHCb by 20 %.