Prospects for b-tagging in ATLAS and tracking commissioning results with cosmic rays

The ability to identify jets containing B hadrons is important for the high-pT physics program of a general-purpose experiment at the LHC such as ATLAS. This capability relies on the very accurate measurements of the parameters of charged tracks provided by the ATLAS Inner Detector. Using millions of cosmic-ray tracks collected during the automn 2008, the ATLAS Inner Detector has been aligned and its tracking performance assessed. Some of the very encouraging results which have been obtained and are relevant for b-tagging are discussed, notably the current level of alignment of the detector and the resolution on the transverse impact parameter of tracks. The various b-tagging algorithms are then described, and their anticipated performance discussed in the light of the cosmic-ray data results. Finaly,the expected accuracy with which the b-tagging performance will be measured in data is mentioned.