Search for Rare B Decays into Two Muons with the ATLAS Detector

Rare B decays have always played a crucial role in shaping the flavour structure of the SM and particle physics in general. Since the first measurement of rare radiative B meson decays by the CLEO Collaboration this area of particle physics has received much experimental and theoretical attention. In particular, FCNC B decays provided crucial tests for the SM at the quantum level, since they are highly suppressed. Hence, these rare B decays are characterised by their high sensitivity to NP. My thesis reports all the studies I performed within the rare B decays ATLAS group, measuring the branching ratio of the B_{s} meson decaying into two muons on data collected by the ATLAS detector during the first period of data taking at the LHC.