We present a measurement of the $CP$-violating weak mixing phase ${\varphi }_s$ using the decay ${\overline{B}}_s^0\to D_s^{+}{D}_s^{-}$ in a data sample corresponding to $3.0{\mathrm{fb}}^{-1}$ of integrated luminosity collected with the LHCb detector in $pp$ collisions at center-of-mass energies of 7 and 8 TeV. An analysis of the time evolution of the system, which does not use the constraint $|\lambda |=1$ to allow for the presence of $CP$ violation in decay, yields ${\varphi }_s=0.02\pm 0.17(\text{stat})\pm 0.02(\text{syst})\text{rad}$, $|\lambda |={0.91}_{-0.15}^{+0.18}(\text{stat})\pm 0.02(\text{syst})$. This result is consistent with the standard model expectation.

• Received 17 September 2014

DOI:https://doi.org/10.1103/PhysRevLett.113.211801

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© 2014 CERN, for the LHCb Collaboration