The Role of the LAr Calorimeter in the Search for H->gamma gamma in ATLAS

In the low mass range (100 to 140 GeV) one of the most promising search channel for the Higgs boson at the LHC is the rare decay in a pair of photons. Photon identification and energy as well as direction measurements are key ingredients to reduce backgrounds and maximize the sensitivity to the Higgs boson signal. The analysis of the Higgs boson search in the two photon decay channel performed by the ATLAS experiment using 4.9 fb$^{-1}$ of proton-proton collisions data recorded in 2011 at the LHC is described. The role of the ATLAS Liquid Argon calorimeter in this analysis is emphasized.