Status of the Fast Interaction Trigger for ALICE Upgrade

The Fast Interaction Trigger (FIT) denotes a set of three new detectors being part of the upgrade of ALICE in preparation for Run 3 of the LHC at CERN. To fulfill its physics objectives, ALICE aims to collect in Run 3 all minimum-bias data at the target interaction rate of 50 kHz for Pb-Pb and up to 1 MHz for pp collisions. This challenging increase in data rates of almost two orders of magnitude compared with Run 1 and Run 2 requires major improvements in all ALICE subdetectors, especially in their readout. While some of the upgraded ALICE detectors can operate in a continuous readout mode others need the fast trigger, specifically: Transition Radiation Detector (TRD), Charged-Particle Veto (CPV), High Momentum Particle Identification (HMPID), calorimeters and Photon Spectrometer (PHOS). Besides generating triggers for them, the FIT detectors will monitor luminosity, will provide the collision start time for particle identification via the time of flight, will measure the particle multiplicity in the forward direction, the centrality and the event plane, and will participate in diffractive physics measurements.The FIT consists of the following three detectors: FT0 - a set of two fast Cherenkov arrays specializing in minimum-bias trigger generation and luminosity measurement, located on both sides of the interaction point; FV0 - a large segmented scintillator disk focusing on multiplicity triggers and event plane determination, attached to the FT0 array located opposite to the Muon Spectrometer; and FDD (Forward Diffractive Detector) - also a scintillator located at very high pseudorapidities, concentrating on background monitoring and diffractive physics. The assembly of FIT detectors is close to completion. All components are on time for installation at ALICE between December 2020 and May 2021 according to the present schedule.