ATLAS High-Level Trigger performance for calorimeter-based algorithms in LHC Run-I

During Run-I of the Large Hadron Collider at CERN the ATLAS detector recorded more than 26 fb$^{-1}$ of proton-proton collision events. One of the key components of the ATLAS detector is its trigger system. In order to keep up with the fast-paced evolution of the beam conditions during Run-I, the trigger selection had to be constantly adapted. For most of the calorimeter-based triggers only modest modifications of the thresholds had to be made, given the change in instantaneous luminosity of five orders of magnitude. This was achieved by various improvements in the High-Level Trigger algorithms, in several places abandoning the original RoI-based concept and introducing new features to overcome previous limitations. The excellent performance of both ATLAS and the LHC made possible the discovery of a new particle already during Run-I, the long-sought Higgs boson.