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

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