ALICE (A Large Ion Collider Experiment) is a general purpose heavy-ion experiment designed for the study of strongly-interacting matter at the extreme energy densities reached in Pb-Pb collisions at the CERN LHC, where the deconfined phase of hadronic matter known as Quark-Gluon Plasma (QGP), is formed.
The innermost detector of ALICE is the Inner Tracking System. In its first release, it consists of six cylindrical layers of silicon detectors based on different technologies: two inner layers of pixel sensors (Silicon Pixel Detector), two intermediate layers of drift sensors (Silicon Drift Detector), two outer layers of strip sensors (Silicon Strip Detector).
The ITS is used for the reconstruction of primary and secondary vertices, for particle tracking, for a precise determination of the impact parameter and for particle identification at low momentum.
In this report, after a brief description of the three subdetectors, the operational experience with the first ITS implementation is summarized, the status and the performance of the detector are described and the lessons learned are discussed after the end of its operation coinciding with the completion of the LHC Run2.