Measurement of the CP-violating phase ϕ_s in Bs0→J/ψϕ decays in ATLAS at 13 TeV

A measurement of the Bs0→J/ψϕ decay parameters using 80.5fb-1 of integrated luminosity collected with the ATLAS detector from 13 Te proton–proton collisions at the LHC is presented. The measured parameters include the CP-violating phase ϕ_s, the width difference Δ Γ _s between the Bs0 meson mass eigenstates and the average decay width Γ _s. The values measured for the physical parameters are combined with those from 19.2fb-1 of 7 and 8 Te data, leading to the following: ϕs=-0.087±0.036(stat.)±0.021(syst.)radΔΓs=0.0657±0.0043(stat.)±0.0037(syst.)ps-1Γs=0.6703±0.0014(stat.)±0.0018(syst.)ps-1Results for ϕ_s and Δ Γ _s are also presented as 68% confidence level contours in the ϕ_s–Δ Γ _s plane. Furthermore the transversity amplitudes and corresponding strong phases are measured. ϕ_s and Δ Γ _s measurements are in agreement with the Standard Model predictions.