Measurement of the CP -violating phase $$\phi _s$$ ϕ s in $$ B_{s}^{0} \rightarrow J/\psi \phi $$ B s 0 → J / ψ ϕ decays in ATLAS at 13 TeV

A measurement of the $$ B_{s}^{0} \rightarrow J/\psi \phi $$ decay parameters using $$ 80.5\, \mathrm {fb^{-1}} $$ of integrated luminosity collected with the ATLAS detector from 13  $$\text {Te}\text {V}$$ proton–proton collisions at the LHC is presented. The measured parameters include the CP-violating phase $$\phi _{s} $$ , the width difference $$ \Delta \Gamma _{s}$$ between the $$B_{s}^{0}$$ meson mass eigenstates and the average decay width $$ \Gamma _{s}$$ . The values measured for the physical parameters are combined with those from $$ 19.2\, \mathrm {fb^{-1}} $$ of 7 and 8  $$\text {Te}\text {V}$$ data, leading to the following: $$\begin{aligned} \phi _{s}= & {} -0.087 \pm 0.036 ~\mathrm {(stat.)} \pm 0.021 ~\mathrm {(syst.)~rad} \\ \Delta \Gamma _{s}= & {} 0.0657 \pm 0.0043 ~\mathrm {(stat.)}\pm 0.0037 ~\mathrm {(syst.)~ps}^{-1} \\ \Gamma _{s}= & {} 0.6703 \pm 0.0014 ~\mathrm {(stat.)}\pm 0.0018 ~\mathrm {(syst.)~ps}^{-1} \end{aligned}$$ Results for $$\phi _{s} $$ and $$ \Delta \Gamma _{s}$$ are also presented as 68% confidence level contours in the $$\phi _{s} $$ – $$ \Delta \Gamma _{s}$$ plane. Furthermore the transversity amplitudes and corresponding strong phases are measured. $$\phi _{s} $$ and $$ \Delta \Gamma _{s}$$ measurements are in agreement with the Standard Model predictions.