Improved Measurement of CP Violation Parameters in Bs0 →j/ψK+K- Decays in the Vicinity of the φ (1020) Resonance

The decay-time-dependent CP asymmetry in Bs0→J/ψ(→μ+μ-)K+K- 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 Bs0 signal decays with an invariant K+K- mass in the vicinity of the φ(1020) resonance, the CP-violating phase φs is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the Bs0-B¯s0 system, ΔΓs, and the difference of the average Bs0 and B0 meson decay widths, Γs-Γd. The values obtained are φs=-0.039±0.022±0.006 rad, ΔΓs=0.0845±0.0044±0.0024 ps-1, and Γs-Γd=-0.056-0.0015+0.0013±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 K+K- system and shows no evidence for polarization dependence.