Precision Measurement of CP Violation in B0s → J/Ψ K+K− Decays

The time-dependent CP asymmetry in B0s → J/ψ K+ K− decays is measured using pp collision data, corresponding to an integrated luminosity of 3.0 fb^−1, collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV. In a sample of 96000 B0s → J/ψ K+ K− decays, the CP-violating phase φs is measured, as well as the decay widths ΓL and ΓH of the light and heavy mass eigenstates of the B0s–antiB0s system. The values obtained are φs = −0.058 ± 0.049 ± 0.006 rad, Γs ≡ (ΓL+ΓH)/2 = 0.6603 ± 0.0027 ± 0.0015 ps^−1, and ΔΓs ≡ ΓL−ΓH = 0.0805 ± 0.0091 ± 0.0032 ps^−1, where the first uncertainty is statistical and the second, systematic. These are the most precise single measurements of those quantities to date. A combined analysis with B0s → J/ψ π+ π− decays gives φs = −0.010 ± 0.039 rad. All measurements are in agreement with the standard model predictions. For the first time, the phase φs is measured independently for each polarization state of the K+ K− system and shows no evidence for polarization dependence.