Top quark pair production cross section studies with the ATLAS detector

A measurement of the top-antitop production cross section in the semileptonic channel will be performed using the first data collected by the ATLAS detector in 2008. In preparation for the measurement, cuts used to discriminate signal from background have been optimized using simulated events and assuming an integrated luminosity of 100 inverse picobarns. The main irreducible background is W+jets production; the uncertainty on the rate of this process has been estimated using simulated samples. The main instrumental background is QCD multijet production; the uncertainty on this background rate is obtained from data. The uncertainty on the luminosity collected by the ATLAS detector during 2008 will be considerable. Further uncertainties due to the jet energy scale, the underlying event, the top quark mass, jet and lepton identification, and trigger performance must also be considered. I discuss the methods used to estimate these uncertainties and their effect on the planned measurement