Measurement of the weak mixing phase ${\varphi }_s$ in B${}_s^0\to$ D${}_s^{+}$ D${}_s^{-}$ decays with the LHCb experiment

One research priority of the LHCb experiment is testing the Standard Model by the precise measurement of CP-violating parameters. In B${}_s^0$-meson decays with b$\to$ $c\overline{c}$s transitions, the weak mixing phase ${\varphi }_s$ can be measured in the interference between the decay with and without B${}_s^0$-$\overline{B_s^0}$ mixing. Since ${\varphi }_s$ is predicted to be small in the Standard Model, a significant deviation to this prediction could be evidence of New Physics. In this talk the current status of the B${}_s^0\to$ D${}_s^{+}$ D${}_s^{-}$ analysis will be presented. The analysis aims to measure ${\varphi }_s$ by using data corresponding to an integrated luminosity of 6 fb${}^{-1}$ collected by the LHCb detector during 2015 to 2018 at a centre-of-mass energy of 13 TeV.