Mixing and CP violation in the Bd and Bs systems at ATLAS

This note includes a measurement of the $B^0_s$ decay parameters in the $ B_s \rightarrow J/\psi$ channel and a measurement of the $B_d$ meson 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 $\phi_s$, the decay width $\Gamma_s$ and the width difference between the mass eigenstates $\Delta \Gamma_s$. The second result presents the measurement of the width difference $\Delta \Gamma_d$, which is extracted from the measurement of the lifetime dependence of $B_d \to J/\psi K_S$ and $B_d \to J/\psi K^{*0}$ decays. The obtained results are $\phi_s = −0.098 \pm 0.084 (\textrm{stat.}) \pm 0.040 (\textrm{syst.})$ rad. and $\Delta \Gamma_d / \Gamma_d = (-0.1 \pm 1.1 (\textrm{stat.}) \pm 0.9 (\textrm{syst.}))\times 10^{-2}$.