New physics searches with B mesons at the ATLAS experiment

The large amount of Heavy Flavour data collected by the ATLAS experiment is potentially sensitive to New Physics, which may be found in the mixing of B meson states, or through processes that are naturally suppressed in the Standard Model. We present the most recent results on the measurement of the decay of the $B_{s}$ into $J/\psi$ $\phi$ based on full data collected in LHC Run-1 and with updated flavour tagging improving the accuracy in the CP-violating phase $\phi_{s}$. We also present the measurement of the decay time difference in the $B_{d}$ system. The most recent results on the search for the rare decay $B_{s}$ ($B^{0}$) $\rightarrow$ $\mu^{+}$ $\mu^{-}$ are presented as well as results on the angular distribution parameters $A_{FB}$ and $F_{L}$ describing the decay $B_{d}$ $\rightarrow$ $K^{*}\mu^{+}\mu^{-}$ $\rightarrow$ $K^{+}\pi^{-} \mu^{+} \mu^{-}$.