Measurement of CP Violation and the B0s Meson Decay Width Difference with B0s → J/ψ K+ K− and B0s → J/ψ π+ π− Decays

The time-dependent CP asymmetry in B0s → J/ψ K+ K− decays is measured using pp collision data at √s = 7 TeV, corresponding to an integrated luminosity of 1.0 fb^−1, collected with the LHCb detector. The decay-time distribution is characterized by the decay widths Γ_L and Γ_H of the light and heavy mass eigenstates of the B0s−antiB0s system and by a CP-violating phase ϕ_s. In a sample of 27617 B0s → J/ψ K+ K− decays, where the dominant contribution comes from B0s → J/ψ ϕ decays, these parameters are measured to be ϕs = 0.07 ± 0.09(stat) ± 0.01(syst) rad, Γ_s ≡ (Γ_L + Γ_H)/2 = 0.663 ± 0.005(stat) ± 0.006(syst) ps^−1, and ΔΓ_s ≡ Γ_L − Γ_H = 0.100 ± 0.016(stat) ± 0.003(syst) ps^−1, corresponding to the single most precise determination of ϕ_s, ΔΓ_s, and Γ_s. The result of performing a combined analysis with B0s → J/ψ π+ π− decays gives ϕ_s = 0.01 ± 0.07(stat) ± 0.01(syst) rad, Γ_s = 0.661 ± 0.004(stat) ± 0.006(syst) ps^−1, and ΔΓ_s = 0.106 ± 0.011(stat) ± 0.007(syst) ps^−1. All measurements are in agreement with the Standard Model predictions.