Angular analysis of the decay $\mathrm{B^{0}}\to \mathrm{K}^{*0} \mu^{+} \mu^{-}$ and studies of mixing and $CP$ violation in the $\bf B_S^0$ system with the ATLAS detector

The measurement of B meson decay properties provides an alternative approach for searches for physics beyond the Standard Model. We present two different measurements performed with data taken in 2011 with the ATLAS detector at the Large Hadron collider. The first measurement is based on an angular analysis of the decay B->K*mumu, and in the second measurement the decay width difference delta_Gamma_S and the weak phase phi_s of the Bs0 system is determined using the decay Bs->JPsiPhi. For the second measurement a probability for the flavour quantum number of the b_quark at production time is determined.