Abstract
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 900 GeV. This was followed by collisions at the unprecedented energy of 7 TeV in March 2010. The SemiConductor Tracker (SCT) is a precision tracking device in ATLAS made up from silicon microstrip detectors processed in the planar p-in-n technology. The signal from the strips is processed in the front-end ASICs working in binary readout mode. Data is transferred to the off-detector readout electronics via optical fibers. The completed SCT has been installed inside the ATLAS experiment. Since then the detector was operated for two years under realistic conditions. Calibration data has been taken and analysed to determine the performance of the system. In addition, extensive commissioning with cosmic ray events has been performed both with and without magnetic field. The sensor behaviour in magnetic field was studied by measurements of the Lorentz angle. After this commissioning phase it arrived to the first LHC pp collision runs in very good shape: 99% of the SCT strips are operational, noise occupancy and hit efficiency exceed the design specifications, the alignment is already close enough to the ideal one to allow online track reconstruction and invariant mass determination.
Highlights
Detector OperationThe SemiConductor Tracker (SCT) detector is operated at a reverse bias voltage of 150 V
During stable proton collisions, the SemiConductor Tracker (SCT) detector is operated at a reverse bias voltage of 150 V
When Large Hadron Collider (LHC) beams are non-stable the bias voltage is reduced to 50 V to minimize the risk of damaging the silicon modules by possible large charge deposits
Summary
The SCT detector is operated at a reverse bias voltage of 150 V. At the beginning of operation full depletion is reached at about 60 V. This will increase with irradiation over the coming years. When LHC beams are non-stable the bias voltage is reduced to 50 V (standby) to minimize the risk of damaging the silicon modules by possible large charge deposits. The modules are operated at different temperatures depending on their position in the detector. They are readout in binary mode, which registers whether or not the signal is above a threshold of 1 fC. A time bin is 25 ns long corresponding to the LHC bunch spacing
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