Measurement of the CKM angle γ and B_s⁰‐B̅_s⁰ mixing frequency with B_s⁰→D_s^∓h^±π^±π^∓ decays

The CKM angle γ is measured for the first time from mixing-induced CP violation between B_s⁰→D_s^∓K^±π^±π^∓ and B̅_s⁰→D_s^±K^∓π^∓π^± decays reconstructed in proton-proton collision data corresponding to an integrated luminosity of 9 fb⁻¹ recorded with the LHCb detector. A time-dependent amplitude analysis is performed to extract the CP-violating weak phase γ − 2β_s and, subsequently, γ by taking the B_s⁰‐B̅_s⁰ mixing phase β_s as an external input. The measurement yields γ = (44 ± 12)° modulo 180°, where statistical and systematic uncertainties are combined. An alternative model-independent measurement, integrating over the five-dimensional phase space of the decay, yields γ=(44−13+20)° modulo 180°. Moreover, the B_s⁰‐B̅_s⁰ oscillation frequency is measured from the flavour-specific control channel B_s⁰→D_s⁻π⁺π⁺π⁻ to be ∆m_s = (17.757 ± 0.007(stat) ± 0.008(syst)) ps⁻¹, consistent with and more precise than the current world-average value.