Mixing and CP Violation in the B_d and B _s Systems at ATLAS

This note includes a measurement of the B ^o _s decay parameters in the B_s → J / ψ ϕ channel and a measurement of the B⁰ meson proper decay time and decay width using the statistics collected by the ATLAS experiment in Run I of the LHC. The first result presents the measurement of the CP -violating phase ϕ_s, the decay width Γ_s and the width difference between the mass eigenstates ΔΓ_s. The second result presents the measurement of the width difference ΔΓ_d, which is extracted from the measurement of the lifetime dependence of B ⁰→ J / ψ K_s and B ⁰→ J / ψ K*° decays. The obtained results are ϕ_s = 0.098 ± 0.084(stat.) ± 0.040(syst.) rad. and ΔΓ_d/Γ_d = (-0.1 ± 1.1(stat.) ± 0.9(syst.)) × 10^-2. (paper)