Measurement of the CP-violating phase φ_s in B⁰_s→J/ψφ decays in ATLAS at 13 TeV

A measurement of the B⁰_s→J/ψφ decay parameters using 80 fb^-1 of integrated luminosity collected with the ATLAS detector from 13 TeV proton-proton collisions at the LHC is presented. The measured parameters include the CP-violating phase φ_s, the width difference △Γ_s between the B⁰_s meson mass eigenstates and the average decay width Γ_s. The values measured for the physical parameters are combined with those from 19.2 fb^-1 of 7 TeV and 8 TeV data, leading to the following:

φ_s = -0.087 ± 0.036 (stat.) ± 0.021 (syst.) rad

△Γ_s = 0.0657 ± 0.0043 (stat.) ± 0.0037 (syst.) ps^-1

Γ_s = 0.6703 ± 0.0014 (stat.) ± 0.0018 (syst.) ps^-1

Results for φ_s and △Γ_s are also presented as 68% confidence level contours in the φ_s-△Γ_s plane. Furthermore, the transversity amplitudes and corresponding strong phases are measured. The φ_s and △Γ_s measurements are in agreement with the Standard Model predictions.