Measurement of the /CP violation phase $\phi_s$ at LHCb

The measurement of the mixing- induced CP- violating phase $\phi_s$ in the $B^0_s$ - $B^0_s$ system is one of the key goals of the LHCb experiment, and provides an excellent opportunity to search for New Physics beyond Standard Model. Using Run-I data, $\phi_s$ has been measured in several decay channels. These proceedings briefly summarise the previous LHCb Run-I results of $\phi_s$ measurement, and show the most recent results obtained by analysing the decay channel $B^0_s \to J/\psi K^+K^-$ in the $K^+K^-$ mass region above the $\phi$ (1020) resonance.