Status and performance of the ALICE Fast Interaction Trigger

Abstract: The ALICE apparatus at CERN has undergone significant upgrade during the LHC's Long Shutdown 2 to increase the experiment's rate capability and measurement precision for Run 3 and Run 4. One of the key detectors newly introduced to the experiment is the Fast Interaction Trigger (FIT). Featuring minimal dead time, FIT provides a comprehensive trigger menu, including the minimum bias trigger with an efficiency exceeding 90 percent in proton-proton collisions. It also provides centrality, event plane, and background measurement capabilities. Precision of the collision time measurements performed by FIT reached remarkable values of 17 ps (sigma) in proton-proton collisions and 4.4 ps (sigma) in Pb-Pb collisions. This paper details FIT's design, performance, and the technical novelties made to meet the stringent environmental requirements of ALICE.