The ATLAS Inner Detector operation,data quality and tracking performance.

The ATLAS Inner Detector comprises silicon and gas based detectors. The Semi-Conductor Tracker (SCT) and the Pixel Detector are the key precision tracking silicon devices in the Inner Detector of the ATLAS experiment at CERN LHC. And the the Transition Radiation Tracker (TRT), the outermost of the three subsystems of the ATLAS Inner Detector is made of thin-walled proportional-mode drift tubes (straws). The Pixel Detector consists of approximately 80 million pixels that are individually read out via chips bump-bonded to 1744 n-in-n silicon substrates. The SCT is a silicon strip detector and is constructed of 4088 silicon detector modules for a total of 6.3 million strips. Each module is designed, constructed and tested to operate as a stand-alone unit, mechanically, electrically, optically and thermally. The SCT silicon micro-strip sensors are processed in the planar p-in-n technology. The signals from the strips are processed in the front-end ASICS ABCD3TA, working in the binary readout mode. The TRT is made of 300000 straw-tubes providing on average 30 two-dimensional space points with ~130 µm resolution for charged particle tracks with |η| < 2 and pT > 0.5 GeV. Along with continuous tracking, the TRT provides electron identification capability through the detection of transition radiation X-ray photons. We will report on the operation of the Inner detector and the data quality during the many months of data taking (the LHC delivered 47pb-1 in 2010 and 5.6fb-1 in 2011 of proton-proton collision data at 7 TeV, and two times one-month periods of heavy ion collisions). The track and vertex reconstruction algorithms of the ATLAS Inner Detector have demonstrated excellent performance since the early data from the LHC. The combination of both silicon and gas based detectors provides high precision impact parameter and momentum measurement of charged particles, with high efficiency and small fake rate. Vertex reconstruction is used to identify with high efficiency the hard scattering process and to measure the amount of pile-up interactions, both aspects are crucial for many physics analyses. The performance of track and vertex reconstruction efficiency and resolution will be presented.