In preparation for the LHC Run 3 ALICE will upgrade its subsystems to cope with the increased interaction rate of 50 kHz in Pb–Pb and up to 1 MHz in other collision systems, resulting in a data throughput from the detector up to 3 TB/s. Storing and analyzing such amount of data is a significant challenge and therefore, online event selection will be required.

The Fast Interaction Trigger (FIT) will generate minimum-bias and multiplicity triggers with maximum latency of 425 ns. It will measure the time of collision with a resolution better than 40 ps. Moreover, FIT will be used to reconstruct the vertex position, forward particle multiplicity, centrality and event plane as well as study diffractive physics.

In this contribution, we present the FIT components, discuss their role in the upgraded ALICE setup and show the results of performance and trigger simulations.