Search for CP violation in the $B^{0}_{s}- \overline{B}^{0}_{s}$ system

We present studies from the LHCb experiment leading to the measurement of the weak phase {\phi}s. At first, flavor tagging is established by measuring the B0s oscillation frequency \Deltams. Then, flavor tagging is used to perform a measurement of the well known CKM angle sin 2{\beta} in B0 \rightarrow J/{\psi} KS0, before we constrain {\phi}s through an amplitude analysis of B0s \rightarrow J/{\psi} {\phi} decays. These studies use about 35 inverse pb of data taken in 2010. In addition, we present the measurement of B(B+\rightarrowJ/{\psi}{\pi}+)/B(B+\rightarrowJ/{\psi}K+) and the first observation of B0s \rightarrowJ/{\psi}f2'(1525).