Data-driven background estimation in ATLAS

The search for charged Higgs with a mass below the top quark mass assumes a production of the Higgs in tt events. This leads to a significant background from a verity of sources common to tt events. As the knowledge of many of these sources is limited, an alternative methods were developed to tackle this systematic barrier. Data driven methods are used to estimate most of the background sources to the charged Higgs searches with the ATLAS detector at the LHC.