Measurement of CP asymmetry in $ {\textrm{B}}_{\textrm{s}}^0\to {\textrm{D}}_{\textrm{s}}^{\mp }{\textrm{K}}^{\pm } $ decays

A measurement of the CP -violating parameters in ${B}_s^0{\to}{D}_s^{\mp }{K}^{\pm}$ decays is reported, based on the analysis of proton-proton collision data collected by the LHCb experiment corresponding to an integrated luminosity of 6 fb − 1 at a centre-of-mass energy of 13 TeV. The measured parameters are obtained with a decay-time dependent analysis yielding C f = 0.791 ± 0.061 ± 0.022, ${A}_f^{\Delta \Gamma}$ = −0.051 ± 0.134 ± 0.058, ${A}_{\overline{f}}^{\Delta \Gamma}$ = −0.303 ± 0.125 ± 0.055, S f = −0.571 ± 0.084 ± 0.023 and ${S}_{\overline{f}}$ = −0.503 ± 0.084 ± 0.025, where the first uncertainty is statistical and the second systematic. This corresponds to CP violation in the interference between mixing and decay of about 8.6 σ . Together with the value of the ${B}_s^0$ mixing phase −2 β s , these parameters are used to obtain a measurement of the CKM angle γ equal to (74 ± 12)° modulo 180°, where the uncertainty contains both statistical and systematic contributions. This result is combined with the previous LHCb measurement in this channel using 3 fb − 1 resulting in a determination of $\gamma ={\left({81}_{-11}^{+12}\right)}^{\circ }$ .