Improved Measurement of CP Violation Parameters in B0s → J=ψK + K − Decays in the Vicinity of the ϕð1020Þ Resonance

The decay-time-dependent CP asymmetry in B0s → J=ψð→ μþμ−ÞKþK− decays is measured using proton-proton collision data, corresponding to an integrated luminosity of 6 fb−1, collected with the LHCb detector at a center-of-mass energy of 13 TeV. Using a sample of approximately 349 000 B0s signal decays with an invariant KþK− mass in the vicinity of the ϕð1020Þ resonance, the CP-violating phase ϕs is
measured, along with the difference in decay widths of the light and heavy mass eigenstates of the B0s - ¯B0s system, ΔΓs, and the difference of the average B0
s and B0 meson decay widths, Γs − Γd. The values obtained are ϕs ¼ −0.039 ± 0.022 ± 0.006 rad, ΔΓs ¼ 0.0845 ± 0.0044 ± 0.0024 ps−1, and Γs − Γd ¼ −0.0056þ0.0013
−0.0015 ± 0.0014 ps−1, where the first uncertainty is statistical and the second
systematic. These are the most precise single measurements to date and are consistent with expectations based on the Standard Model and with the previous LHCb analyses of this decay. These results are combined with previous independent LHCb measurements. The phase ϕs is also measured independently for each polarization state of the KþK− system and shows no evidence for polarization dependence.