The Fast Interaction Trigger Upgrade for ALICE

Abstract

The ALICE Collaboration is preparing a major detector upgrade for the second LHC long shutdown . The LHC heavy-ion luminosity and collision rate from 2021 onwards will considerably exceed the design parameters of the present ALICE forward trigger detectors. Furthermore, the introduction of a new Muon Forward Tracker (MFT) will significantly reduce the space available for the upgraded trigger detectors. To comply with these conditions a Fast Interaction Trigger (FIT) has been designed. FIT will be the primary forward trigger, luminosity, and collision time measurement detector. The FIT will be capable of triggering at an interaction rate of 50 kHz, with a time resolution better than 30 ps, with 99% efficiency. It will also determine multiplicity, centrality, and reaction plane. FIT will consist of two arrays of Cherenkov radiators with MCP-PMT sensors and of a single, large-size scintillator ring. The arrays will be placed on both sides of the interaction point (IP). Because of the presence of the hadron absorber of the muon spectrometer, the placement of the FIT detectors will be asymmetric: one array at about 800 mm from the IP on the absorber side and and the other array together with the scintillator ring at around 3200 mm from IP on the opposite side. Scheduled for installation in 2020, FIT is in the midst of an intense R&D and prototyping period. The timing, amplitude and efficiency characteristics are determined with relativistic particles and with lasers. The ongoing Monte Carlo studies verify the physics performance and refine the geometry of the FIT arrays. This report gives a short description of FIT, a summary of the performance, and the outcome of the simulations and beam tests.