Study of the Material Budget in the ATLAS Inner Detector with K0S decays in collision data at sqrt(s)=900 GeV

The precise knowledge of material in the ATLAS Inner Detector is vital for understanding tracking performance and thus important for many physics analyses. A powerful approach to estimate the material in data is to study well-known particle decays reconstructed in the tracking volume. In this note, the reconstructed invariant mass of Kshort in decays to two charged pions is used to quantify the material description using data from the sqrt(s) = 900 GeV run of 2009. Full Monte Carlo simulation samples with additional material added are used to study and calibrate the impact of unaccounted material on the invariant mass. The nominal Monte Carlo simulation is found to describe accurately the Inner Detector material budget and no evidence for unaccounted material is found within the Pixel up to |eta|<2.