ATLAS Silicon Microstrip Tracker Operation and Performance

The Semi-Conductor Tracker (SCT) is a silicon strip detector and one of the key precision tracking devices in the Inner Detector (ID) of the ATLAS experiment at CERN LHC. The SCT is constructed of 4088 silicon detector modules with 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 modules are mounted into two types of structures: one barrel (4 cylinders) and two end-cap systems (9 disks on each side of the barrel). The SCT silicon microstrip 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. Data is transferred to the off-detector readout electronics via optical fibres. SCT has been installed inside the ATLAS experimental cavern since 2007 and has been operational ever since. Calibration data has been taken regularly and analysed to determine the noise performance of the system. Extensive commissioning with cosmic ray events has been performed both with and without a magnetic field. The sensor behaviour in the 2 Tesla solenoid magnetic field was studied by measurements of the Lorentz angle. We find 99.3% of the SCT modules are operational, noise occupancy and hit efficiency exceed the design specifications and the alignment is very close to the ideal to allow on-line track reconstruction and invariant mass determination. The current results from the successful operation of the SCT detector and its status after three years of operation are presented. We report on the operation of the detector including an overview of the issues we encountered and the observation of significant increases in leakage currents (as expected) from bulk damage due to non-ionising radiation. The main emphasis is given to the tracking performance of the SCT and the data quality. The running experience will then be used to extract valuable lessons for future silicon strip detector projects.