CP violation in Bs mixing

This note reports about the measurements of CP violation in the B s system by the ATLAS, CMS, and LHCb experiments at LHC. The main experimental challenges and techniques are briefly summarized. The results published so far by the three experiments are shown, stressing in particular those on the weak phase s , which is measured in B s J/ events by ATLAS and LHCb to be s = 0.12 0.23 0.11 rad and s = 0.07 0.09 0.01 rad respectively. The efforts done by the three experiments to obtain a more precise determination of s and of the other observables are described, giving some prospects on the potential improvements that can be achieved with the Run II of LHC.