Photon/jet separation with DC1 data

Results on the photon identification and QCD-jet rejection capabilities of the {\\sc Atlas} detector are presented. The simulation, reconstruction and analysis are done in the framework of Data Challenge 1. This study is based on fully simulated events at the initial low ($2\\times 10^{33} {\\rm cm^{-2}\\ s^{-1}}$) and design high ($10^{34} {\\rm cm^{-2}\\ s^{-1}}$) luminosity, on which pile-up is superimposed. A jet rejection factor of about 5000-6000 for $p_T>25$ GeV can be obtained for a photon identification efficiency $\\sim 80\\%$. The application of this rejection to the fake background in the $H\\rightarrow\\gamma\\gamma$ analysis is discussed.