Studies of suppressed processes in B mesons decays and of mixing/CP violation in the Bs system with the ATLAS detector

Evidence for New Physics signatures is searched in processes that are naturally suppressed in the Standard Model. Recent results on the angular distribution parameters AFB and FL describing the decay Bd -> K*mu+mu- -> K+pi-mu+mu- are presented. The accuracy obtained from data collected in 2011 is comparable to the best previous measurement in the region q^2(mu+mu-)>16 GeV^2. New results on the search for the rare decay Bs (B0) -> mu+mu- are presented.