ALICE ITS2 - A Monolithic Active Pixel Sensor based Inner Tracking System for ALICE

About

During the long shutdown 2 of the LHC, ALICE installed a new Inner Tracking System (ITS2), replacing the previous one. The new ITS2 is entirely based on Monolithic Active Pixel Sensors called ALPIDE. It has an active area of 10m2 segmented in 12.5 billion pixels with a pitch of 27μm x 29μm. Moving the innermost layer closer to the beam pipe, increasing granularity and reducing the material budget are the main elements of the strategy to improve the impact-parameter resolution and tracking efficiency at low transverse momentum with respect to the previous tracker. In addition to the increased precision, ITS2 is able to cope with the increased Pb-Pb interaction rate of 50 kHz planned for Run 3. After the completion of the assembly in December 2019, the detector was commissioned on surface using the final services throughout 2020. In 2021, the detector was first installed in the cavern and then commissioned inside the ALICE apparatus. In this seminar, lessons learned and challenges overcome during construction, on-surface commissioning and installation in the experimental apparatus as well as first results from the commissioning with beam will be presented.