Probing the material in front of the ATLAS electromagnetic calorimeter with energy flow from sqrt(s)=7 TeV minimum bias events

In early April 2010, ATLAS collected several million of minimum bias events at a center of mass energy of 7 TeV. Counting the number of energy deposits above 5 times the measured electronic noise in all electromagnetic calorimeter cells allows a channel by channel check of the response to physics. A readout cabling inversion and a high voltage cable swap, affecting 0.4% of the total number of cells in the region |eta|<2.5, were identified and corrected. The method is also sensitive to the total amount of material in front of the calorimeter, complementing other analyses which are only sensitive to the tracker material. The amount of material of the inner detector services running at constant phi in front of the barrel calorimeter, representing ~0.2 X0, is found in good agreement between data and simulations. Up to 1 X0 lack of material in the ATLAS description has been observed in the localised regions close to the rails supporting the inner detector, which can be fed into new Monte Carlo geometry.