Measurement of the CP-violating phase ϕ_s from B_s ⁰→J/ψπ⁺π⁻ decays in 13 TeV pp collisions

Decays of B_s ⁰ and B‾⁰ _s mesons into J/ψπ⁺π⁻ final states are studied in a data sample corresponding to 1.9 fb⁻¹ of integrated luminosity collected with the LHCb detector in 13 TeV pp collisions. A time-dependent amplitude analysis is used to determine the final-state resonance contributions, the CP-violating phase ϕ_s=−0.057±0.060±0.011 rad, the decay-width difference between the heavier mass B_s ⁰ eigenstate and the B⁰ meson of −0.050±0.004±0.004 ps⁻¹, and the CP-violating parameter |λ|=1.01_−0.06 ^+0.08±0.03, where the first uncertainty is statistical and the second systematic. These results are combined with previous LHCb measurements in the same decay channel using 7 TeV and 8 TeV pp collisions obtaining ϕ_s=0.002±0.044±0.012 rad, and |λ|=0.949±0.036±0.019.