Precision measurements of B -meson decays at ATLAS

The precise measurement of the CP -violating phase ϕ s , the average decay width Γ s and the difference between the widths of the light and heavy mass eigenstates ΔΓ s is presented in the $${B_s^0} $$ → J /ψ ϕ decay channel. Data of pp collisions at √ s = 13 TeV are used, corresponding to 80.5 fb −1 of integrated lu-minosity collected by the ATLAS detector at the Large Hadron Collider in years 2015–2017. Results are statistically combined with the previous measurement with 19.2 fb −1 data with 7 and 8 TeV energy. The measured values are: ϕ s = −0.087 ± 0.036 (stat.) ± 0.021 (syst.) Γ s = 0.6703 ± 0.0014 (stat.) ± 0.0018 (syst.) ΔΓ s = 0.0657 ± 0.0043 (stat.) ± 0.0037 (syst.). Moreover, a study estimating the ATLAS detector performance in measuring the CP -violating phase ϕ s after the HL-LHC upgrade is presented.