On 15 March 100 physicists and engineers gathered in the ALICE underground cavern to witness the end of a 15 year journey of development, construction, commissioning and testing before the Inner Tracking System (ITS) was inserted into the time projection chamber (TPC) at the heart of the experiment. Using the smallest amounts of the lightest material, the ITS has been made as lightweight and delicate as possible.
The ITS comprises six layers of high-precision silicon detectors, with double-sided silicon strips in the outer two layers, silicon drift detectors in the middle two layers and silicon pixels in the two inner layers. With almost 5 m2 of double-sided silicon strip detectors and more than 1 m2 of silicon drift detectors, it is the largest system using both types of silicon detector.
The silicon layers were integrated in Utrecht and Torino for a testing phase before being moved to the ALICE underground cavern. Passing the ITS through the TPC was challenging, with barely enough room for it to fit inside. It took two hours to move just a few dozen metres. The four outermost layers have been installed and the silicon pixel detector is scheduled to be installed this summer.