ALICE ITS2: performance and operational experience

초록

The Inner Tracking System (ITS2) is the innermost tracking detector of the ALICE experiment, upgraded for LHC Run 3, providing vertex reconstruction and tracking of charged particles. The detector consists of seven cylindrical layers of Monolithic Active Pixel Sensors covering 10 m2 of active area and has been successfully operating since 2021. The ALPIDE sensors, manufactured using a 180 nm CMOS technology, feature 29 × 27 µm pixels with a spatial resolution of 5 µm. Thanks to a very light support structure and thinning down the chip thickness to 50 µm, the material budget was reduced to 0.36 % X0 per layer in the Inner Barrel. This contribution reports on three years of ITS2 operational experience during LHC Run 3. Performance results demonstrate excellent detector stability with fake-hit rates below 10−6/pixel/event, detection efficiency exceeding 99 %, and stable threshold operation through occasional retuning. Beam-induced background effects observed in the 2023 heavy-ion run, affecting approximately 10 % of data before mitigation, are reported. Furthermore, the ITS color run campaign successfully demonstrated particle identification capabilities, achieving π/K/p separation through Time-over-Threshold measurements with modified front-end electronics settings and readout configurations. © Copyright owned by the author(s)