Measurement of CP asymmetry in B0 s → D∓ s K± decays

A measurement of the CP-violating parameters in B0 s → D∓ s K± 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 Cf = 0.791 ± 0.061 ± 0.022, A∆Γ f = −0.051 ± 0.134 ± 0.058, A∆Γ f¯ = −0.303 ± 0.125 ± 0.055, Sf = −0.571 ± 0.084 ± 0.023 and Sf¯ = −0.503 ± 0.084 ± 0.025, where the frst 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 B0 s mixing phase −2βs, 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 γ = (81+12 −11) ◦ .