ttbar backgrounds in charged Higgs boson searches

Top quark pair production is the main background for searches in most charged Higgs boson channels. The characteristics of this background are discussed, and the results from ATLAS top quark searches with early LHC data are presented. In the light of charged Higgs boson searches, the different ttbar decay modes can be separated into irreducible ttbar modes with the same final state as the signal, and reducible modes which contribute e.g. if an electron is misreconstructed as a tau. Techniques to suppress and estimate the ttbar background contribution to the charged Higgs boson searches are introduced.