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

Abstract

A measurement is presented of decay-time-dependent CP violation in the decays B⁰ → J/ψ K_S⁰ and B⁰ → ψ(2S)K_S⁰, 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 beCB0→J/ψKS0=0.12±0.07±0.02,SB0→J/ψKS0=0.83±0.08±0.01,CB0→ψ2SKS0=−0.05±0.10±0.01,SB0→ψ2SKS0=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−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 B⁰ → J/ψ K_S⁰ decays, where the J/ψ meson was reconstructed from two muons. The averages of all three sets of LHCb results areCB0→cc¯KS0=−0.017±0.029,SB0→cc¯KS0=0.760±0.034,under the assumption that higher-order contributions to the decay amplitudes are negligible. The uncertainties include statistical and systematic contributions.