Photon Conversions at $\sqrt{s} = 900 \GeV$ measured with the ATLAS Detector

This note presents the first study of converted photons reconstructed with the ATLAS detector in the $\sqrt{s}$ = 900 GeV run in 2009. The analysis of the photon conversions demonstrates the excellent performance of the conversion reconstruction algorithm. The three dimensional distribution of the photon conversion vertices has been extracted and used to provide a first cross-check of the amount of material in the ATLAS tracker using collision data. A few Dalitz decays from neutral mesons have also been reconstructed and their rate is in agreement with expectations from simulation. Finally, the $\pi^0$ mass peak has been extracted from pairs of one converted and one unconverted photon.