Updated measurement of time-dependent CP-violating observables in B_s⁰→J/ψK⁺ K^- decays

The decay-time-dependent CP asymmetry in B_s⁰→J/ψK⁺K^- decays is measured using proton–proton collision data, corresponding to an integrated luminosity of 1.9fb^-1, collected with the LHCb detector at a centre-of-mass energy of 13TeV in 2015 and 2016. Using a sample of approximately 117 000 signal decays with an invariant K⁺K^- mass in the vicinity of the ϕ(1020) resonance, the CP-violating phase ϕ_s is measured, along with the difference in decay widths of the light and heavy mass eigenstates of the B_s⁰-B̅_s⁰ system, ΔΓ_s. The difference of the average B_s⁰ and B⁰ meson decay widths, Γ_s- Γ_d, is determined using in addition a sample of B→J/ ψK⁺π^- decays. The values obtained are ϕ_s=-0.083±0.041±0.006rad, ΔΓ_s=0.077±0.008±0.003ps^-1 and Γ_s-Γ_d=-0.0041±0.0024±0.0015ps^-1, where the first uncertainty is statistical and the second systematic. These are the most precise single measurements of these quantities to date and are consistent with expectations based on the Standard Model and with a previous LHCb analysis of this decay using data recorded at centre-of-mass energies 7 and 8 TeV. Finally, the results are combined with recent results from B_s⁰→J/ψπ⁺π^- decays obtained using the same dataset as this analysis, and with previous independent LHCb results.