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 $B_s \rightarrow J/\psi\phi$decaysarepresentedusing4.9fb$^{-1}$of$pp$ data at $\sqrt{s}$ = 7 TeV from 2011. The methods, their performance and calibration on self-tagged $B^{\pm }\to J\mathrm{/}\psi K^{\pm }$ data are shown.