Higgs Boson Searches @ LHC: Dedicated to Engin

The Higgs boson is the only particle missing to complete the successful description of the elementary ingredients of our world. Its existence and its associated mechanism are predicted by the Standard Model (SM) in order to help give masses to the otherwise massless elementary particles. As of yet, it escapes experimental detection despite the enormous worldwide efforts. The new Large Hadron Collider (LHC) at CERN will provide enough collision energy for its formation, if it exists. The large experiments already installed are equipped with excellent detector capabilities in order to confirm (or reject) its existence. The late Professor Engin Arik and her group have strongly contributed to decade-long efforts of the ATLAS detector realization. The mass of the Higgs boson is not predicted by the SM, but in any case, it is above the existing experimental lower bound of 114.4 GeV/c2 at 95%CL. The Higgs particle decays in a number of different ways. Depending on its mass, different decay modes and decay particle identification capabilities will be exploited for the Higgs possible detection, resulting to the most sensitive discovery potential. Discovery examples for each mass region will be given using the complete - as built - detector simulation and the latest theoretical cross-section calculations as well as, optimized selection criteria and statistical treatment. Furthermore, the sensitivity for the extension of the SM mo del, the MSSM Higgs bosons will be shortly reviewed. Emphasis will be given to the expected discovery potentials from the first years of running