Measurement of CP violation in B 0 → J/ ψK S 0 and B 0 → ψ(2 S) K S 0 decays

Abstract

A measurement is presented of decay-time-dependent CP violation in the decays B 0 → J/ ψ K S 0 and B 0 → ψ(2 S) K S 0 , where the J/ ψ is reconstructed from two electrons and the ψ(2 S) 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({B}^0\to J/ψ {K}S^0)=0.12± 0.07± 0.02, {}S({B}^0\to J/ψ {K}S^0)=0.83± 0.08± 0.01, {}C({B}^0\to ψ (2S){K}S^0)=-0.05± 0.10± 0.01, {}S({B}^0\to ψ (2S){K}S^0)=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 {B}^0-{\overline{B}}^0 oscillation. The first uncertainties are statistical and the second are systematic. The two sets of results are compatible with the previous LHCb measurement using B 0 → J/ ψ K S 0 decays, where the J/ ψ meson was reconstructed from two muons. The averages of all three sets of LHCb results are C({B}^0\to [c\overline{c}]{K}S^0)=-0.017± 0.029, {}S({B}^0\to [c\overline{c}]{K}S^0)=0.760± 0.034, under the assumption that higher-order contributions to the decay amplitudes are negligible. The uncertainties include statistical and systematic contributions.