Measurement of $CP$ asymmetry in $B_s^0\to D_s^{\mp }{K}^{\pm }$ decays

We report the measurements of the $CP$-violating parameters in $B_s^0 \to D_s^{\mp} K^{\pm}$decaysobservedin$pp$ collisions, using a data set corresponding to an integrated luminosity of $3.0{\text{fb}}^{-1}$ recorded with the LHCb detector. We measure $C_f=0.73\pm 0.14\pm 0.05$, $A^{\Delta \Gamma}f = 0.39 \pm 0.28 \pm 0.15$,$A^{\Delta \Gamma}{\overline{f}} = 0.31 \pm 0.28 \pm 0.15$,$S_f = -0.52 \pm 0.20 \pm 0.07$,$S_{\overline{f}} = -0.49 \pm 0.20 \pm 0.07$, where the uncertainties are statistical and systematic, respectively. These parameters are used together with the world-average value of the $B_s^0$ mixing phase, $-2{\beta }_s$, to obtain a measurement of the CKM angle $\gamma$ from $B_s^0\to D_s^{\mp }{K}^{\pm }$ decays, yielding $\gamma = (128,_{-22}^{+17})^\circ$modulo$180^\circ$, where the uncertainty contains both statistical and systematic contributions. This corresponds to $3.8\sigma$ evidence for $CP$ violation in the interference between decay and decay after mixing.