ATLAS silicon microstrip detector operation and performance

In December 2009 the ATLAS experiment at the CERN Large Hadron Collider (LHC) recorded the first proton-proton collisions at a centre-of-mass energy of 900GeV, followed by the unprecedented energy of 7 TeV in March 2010. The Semi-Conductor Tracker (SCT) is a key precision tracking device in ATLAS, made of p-in-n-type silicon micro-strip detectors. The completed SCT has been installed inside the ATLAS experimental hall. After the commissioning phase it was in very good shape for the first LHC collision runs: 99.3% of the SCT strips are operational, noise occupancy and hit efficiency exceed the design specifications, and the alignment is already close enough to the ideal one to allow on-line track reconstruction and invariant mass determination. This paper reviews the current status of the SCT, including results from the latest data-taking periods in 2009 and 2010, and from the detector alignment. The operation of the detector and observed problems are discussed, with emphasis on the performance of the SCT with the LHC in collision mode in comparison with the expected parameters and with the Monte Carlo simulations.