Measurement of $B_{s}$ using $J/\psi \pi^{+}\pi^{-}$ at LHCb

The measurement of violating phase $phi_{s}$ is one of the key goals of the LHCb experiment. It will be performed via a time-dependent amplitude analysis. This poster summaries the measurement of $phi_s$ using $B_{s}\to J/\psi \pi{+}\pi^{-}$ at LHCb using Run-I and years 2015-2016 of Run-II data. The results are compatible with SM predictions.