PoS - Proceedings of Science
Volume 448 - The 32nd International Workshop on Vertex Detectors (VERTEX2023) - Operational experience on current detectors
Operation and Performance of the Upgraded ALICE Inner Tracking System
A.S. Triolo
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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 readout-rate increased from 1 kHz up to 100 kHz in Pb–Pb collisions and 200 kHz in
proton–proton collisions.
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