Determination of \DG by ATLAS and the impact of non-zero \DG on other Bs studies.

ATLAS can measure \DG a decay rate difference between the two mass eigenstates of \Bs - \aBs system, by analysing an angular-time distribution in the cascade decay \Bsto. For a luminosity of $10^{33} cm^{-2} s^{-1}$ a maximum likelihood estimate gives a relative error better than 18\% with a simultaneous measurement of the average \Bs decay rate and the helicity amplitude parameters. The influence of a non-zero \DG value is discussed for \Bs oscillation measurement with flavour specific states and for CP-parity violating asymmetry measurement using tagged \Bst decays.