Mixing and CP violation in the Bs system with ATLAS.

The different amplitudes contributing to the decay of the Bs into J/psi phi (mu+mu-K+K-) are studied with a combined analysis of decay time and angular correlations. The width difference between the Bs eigenstates DeltaGamma_s and the average width Gamma_s are measured with accuracy comparable to the best previous results. New results are presented, where flavor tagging is now exploited to increase the sensitivity to the CP-violating phase phi_s, which is sensitive to New Physics affecting the composition of the Bs mass eigenstates.