$B^0_s \to J/\psi \phi$ in ATLAS

A measurement of the $B^0_s \to J/\psi \phi$ decay parameters using $80.5\,\mathrm{fb}^{-1}$ of integrated luminosity collected with the ATLAS detector from $13\,\mathrm{TeV}$ 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 $B^0_s$ mass eigenstates and the average decay width $\Gamma_s$.