Expected Performance of the ATLAS Inner Detector

The ATLAS experiment at the CERN Large Hadron Collider (LHC) has started taking data in September 2008 with the inauguration of the LHC. Since then, the detector has been commissioned and calibrated in the ATLAS cavern. The ATLAS Inner Detector (ID) placed within a 2 T solenoid magnetic field, is a tracking system for charged particles based on three technologies: silicon pixels, silicon micro-strips and straw drift tubes. The LHC physics discovery potential sets stringent requirements on the performance of the ID, specially in terms of pattern recognition, tracking, momentum and vertex resolution and low radiation length to minimize the material effects. After a brief description of the detector design, the expected performance for identifying and reconstructing single particles with transverse momentum pT > 0.5 GeV is described as well as the detector’s vertexing and b-tagging capabilities. Finally, cosmic ray results that verify so far that the detector is ready to fulfill the expected performance specifications are outlined.