After years of design, construction and commissioning, the two outer detectors – the transition radiation tracker (TRT) and the semiconductor tracker (SCT) – of the inner detector barrel were moved to the ATLAS cavern from the nearby cleanroom at the end of August. The journey was only about 100 m, but it required weeks of planning and a bit of luck concerning the weather. Special measures were in place to minimize shock and vibration during transportation. Accelerometers fitted to the barrel to provide real-time monitoring recorded no values greater than 0.1 g, satisfying the transport specification for this extremely precise and fragile detector. Then, with only a few millimetres of clearance, the detector was inserted into the liquid-argon calorimeter cryostat.
The SCT and TRT are two of the three major parts of the ATLAS inner detector. The innermost layer (pixels) will be installed in 2007. The barrel part of the inner detector containing the two outer subsystems was assembled in February and passed through complete characterization of its performance during tests in spring. An eighth of the TRT and a quarter of the SCT were equipped with complete readout chains, and during testing particular attention was paid to ensuring that the SCT did not generate noise in the TRT and vice versa. The results were a triumph for the designers – mechanical engineers, electronics engineers and physicists. The two detectors, which are completely independent, can operate at thresholds close to that defined by thermal noise.
