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$_{s}^{0}$ → D$_{s}^{∓}$ K$^{±}$ decays observed in pp collisions, using a data set corresponding to an integrated luminosity of 3.0 fb$^{−1}$ recorded with the LHCb detector. We measure C$_{f}$ = 0.73 ± 0.14 ± 0.05, A$_{f}^{ΔΓ}$ = 0.39 ± 0.28 ± 0.15, $ {A}_{\overline{f}}^{\varDelta \varGamma }=0.31\pm 0.28\pm 0.15 $ , S$_{f}$ = −0.52 ± 0.20 ± 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, −2β$_{s}$ , to obtain a measurement of the CKM angle γ from B$_{s}^{0}$ → D$_{s}^{∓}$ K$^{±}$ decays, yielding γ = (128$_{− 22}^{+ 17}$ )° modulo 180°, where the uncertainty contains both statistical and systematic contributions. This corresponds to 3.8 σ evidence for CP violation in the interference between decay and decay after mixing.