Operation and Performance of the Upgraded ALICE Inner Tracking System

The ALICE Experiment underwent a major upgrade during the Long Shutdown 2 of the Large Hadron Collider (LHC), which included the installation of a new Inner Tracking System (ITS2). The ITS2, consisting of a 7-layer, pixel-only tracker with 24,000 Monolithic Active Pixel Sensors (MAPS) and 12.5 billion pixels, represents the largest scale application of the MAPS technology in a high-energy physics experiment to date. It has been successfully commissioned for the LHC Run 3, started in July 2022 with proton–proton collisions at a center of mass energy of 13.6 TeV. To ensure stable operation and maintain high data quality, a regular calibration of the detector has to be performed, which consists in tuning and a subsequent measurement of pixel thresholds and determination of the noisy channels. The complexity of the calibration depends linearly on the number of pixels, making the ITS2 calibration an unprecedented challenge. This work offers an overview of the operational procedures required to maintain optimal detector performance, along with results obtained from calibration and the performance achieved during LHC Run 3. Furthermore, this contribution discusses the significant improvements brought by the ITS2 to the ALICE experiment, such as an impact parameter resolution of about 40 μm both in the 𝑟𝜑 and 𝑧 coordinates at a transverse momentum of 500 MeV/𝑐, a detection efficiency better than 99%, and the event readout-rate increased from 1 kHz up to 100 kHz in Pb–Pb collisions and 200 kHz in proton–proton collisions.