Measurements of $CP$ violation in neutral B mesons at LHCb

During 2011 and 2012 the LHCb detector collected data comingfrom proton-proton collision corresponding to an integrated luminosity of 1 $fb^−1$ at a center-of-mass energy of 7 TeV and 2 $fb^−1$ at a center-of-mass energy of 8 TeV,respectively. Using this data sample LHCb can measure with an unprecedentedprecision the parameters associated to the CKM matrix. In the neutral B mesonsystem,CPviolation is induced from the interference of decay with or without mix-ing, with possible implications in the search for physics beyond the Standard Model.Recent results obtained by LHCb Collaboration are presented, which give access to the β and $\phi_s$ parameters, in particular the analysis of the decays $B^0 \rightarrow J/\psi K_s^0$, $B_s^0 \rightarrow J/\psi K^+K^-$ and $B_s^0 \rightarrow J/\psi \pi ^+\pi^-$. Finally the first LHCb measurements of CP violation in the channels $B^0→D^+D^−$ and $B_s^0→D_s^+ K^−$ are presented.