Flavour tagging techniques for CPV studies in the $B_s$ system with ATLAS

The sensitivity to $B_s$ meson mixing phenomena can be significantly improved by distinguishing the initial meson flavour. The flavour tagging techniques used in the ATLAS measurement of the angular amplitudes contributing to $B_s \rightarrow J/\psi\phi$ decays are presented using 4.9 fb$^{-1}$ of $pp$ data at $\sqrt{s}$ = 7 TeV from 2011. The methods, their performance and calibration on self-tagged $B^\pm \rightarrow J/\psi K^\pm$ data are shown.