Abstract : ATLAS is one of the four experiments operating at the Large Hadron Collider. It was conceived to discover the missing piece of the Standard Model of particle physics, the Higgs boson, and to unveil hints of new physics at the Teraelectron volt scale. The electromagnetic calorimeter, one of the major ATLAS subsystem, uses a liquid argon technology with an accordion geometry. This detector was tested, during construction, in a serie of beam tests and later, after its installation, with cosmic muons. The calorimeter physics performances, such as energy resolution, linearity and uniformity, have been studied. If new physics is found at the LHC, the reconstruction of the underlying theory will be the next challenge. Using the example of the TeV-scale supersymmetric Lagrangian, we show how it is possible, thanks to the SFitter program, to study a high-dimensional likelihood map and extract parameter values and confidence levels. Secondary minima and correlations between the parameters are discussed.