CP violation in Bs mixing at LHCb

The CP violating phase ${\varphi }_s$ can be measured in the interference between mixing and decay of $B_s^0$ mesons decaying to CP eigenstates. The phase ${\varphi }_s$ the decay width difference $\mathrm{\Delta }{\mathrm{\Gamma }}_s$ and the average decay width ${\mathrm{\Gamma }}_s$ have been measured at LHCb, using the full 1 fb${}^{-1}$ of $pp$ collisions data at a centre-of-mass energy $\sqrt{s}$ = 7 TeV collected during the 2011 LHC run.