Search for extra dimension in the diphoton final state with ATLAS

The search for evidence of extra dimensions in the diphoton final states from pp collision at $sqrt{s} = 7$ TeV at the Large Hadron Collider, carried out by the ATLAS experiment, is presented. The various analysis steps, from the event selection and the efficiency estimation, to the evaluation of the reducible and irreducible backgrounds as well as the statistical treatement are discussed. The data sample analysed allows to improve the current limits on the mass of the lightest Randall-Sundrum graviton and on the parameters of the ADD large extra dimension scenario.