Mixing and CP violation in the $B_s$ system with ATLAS

We present a flavour tagged time dependent angular analysis of the $B_s \rightarrow J/\psi\phi$ decay, using 4.9 fb$^{−1}$ of integrated luminosity collected by the ATLAS detector from 7 TeV proton-proton collisions recorded in 2011. CP violation in this channel is described by a weak phase $\phi_s$, which is sensitive to new physics contributions. The measured value is $\phi_s$ = 0.12 $\pm$ 0.25 (stat.) $\pm$ 0.11 (syst.) rad, which is in good agreement with Standard Model expectations. Also other measured parameters are consistent with the world average.