Electron and photon reconstruction and identification in ATLAS: expected performance at high energy and results at 900 GeV

This note presents the first study of electron and photon candidates in the 900 GeV collision data collected by ATLAS at the end of 2009, the collision events analysed corresponding to a total integrated luminosity of approximately 9 μb$^{-1}$. Good agreement is demonstrated between observation and expectation for low-pT electron and photon reconstruction and identification. The expected performance of the reconstruction and identification algorithms used for this purpose and optimised for high-pT physics are described for reference in the first part of this note.