Measurement of CP violation and the Bs0 meson decay width difference with Bs0→J/ψK⁺K^- and Bs0→J/ψπ ⁺π ^- Decays

The time-dependent CP asymmetry in Bs0→J/ψK ⁺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 Bs0-B̄s0 system and by a CP-violating phase _s. In a sample of 27 617 Bs0→J/ψK ⁺K ^- decays, where the dominant contribution comes from Bs0→J/ψ decays, these parameters are measured to be _s=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 _s, ΔΓ _s, and Γ _s. The result of performing a combined analysis with Bs0→J/ψπ ⁺π ^- decays gives _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.