The LHC machine is a 14 TeV proton-proton collider to be installed in the 26.6 km circumference tunnel currently used by the LEP electron-positron collider at CERN. The 7 TeV proton bunches in LHC are separated by 25ns with an RMS intersect length of 75mm inside the experiments. The peak luminosity of LHC is 1034cm-2s-1. This corresponds to around 18 minimum-bias pile-up events per bunch crossing at peak luminosity. The cross-sections and branching ratios of some of the most interesting physics topics to be studied at LHC are such that several years of full luminosity will be needed. As a result of the considerations above, the detectors have to be fast, radiation resistant, with high granularity and good spatial and energy resolution, and cover as much as possible of the full solid angle.
The ATLAS experiment is being constructed for start-up in year 2005. The two magnet systems in ATLAS are a 2 Tesla inner superconducting solenoid around the inner detector cavity, and large superconducting air-core toroids consisting of independent coils outside the calorimetry. The Inner Detector consists of a silicon pixel and microstrip tracker (the silicon microstrip system is referred to as the SCT in the following) surrounded by a straw tube tracker. The calorimeter system is based on Liquid Argon (LAr) electromagnetic calorimeters. The hadron endcap calorimenter and the forward calorimeters are also based on Liquid Argon. The bulk of the hadron calorimetry (barrel and extended barrels) consists of scintillator tile calorimeters. The muon spectrometer in the air-core magnetic field defines the size the detector. The ATLAS detector system is shown below. The Norwegian groups work in ATLAS Inner Detector and more specifically with the ATLAS SCT.
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