# The Fast Interaction Trigger detector for the upgrade of the ALICE experiment at CERN: design and performance

## TL;DR

The paper presents the design, construction, and performance evaluation of the Fast Interaction Trigger (FIT) detector upgrade for the ALICE experiment at CERN, enhancing trigger efficiency, luminosity measurement, and event characterization amid increased collision rates.

## Contribution

It introduces a novel FIT detector system that improves trigger efficiency and measurement capabilities for the upgraded ALICE experiment at CERN.

## Key findings

- Achieved >90% trigger efficiency for pp collisions
- Demonstrated detector's ability to sustain high interaction rates
- Validated performance through beam tests and simulations

## Abstract

ALICE (A Large Ion Collider Experiment) experiment at CERN LHC is designed to study the properties of the Quark-Gluon Plasma (QGP) in heavy-ion collisions. In 2019-2020 the upgrade of CERN LHC will increase the luminosity and the collision rate beyond the design parameters of the current ALICE setup. To be able to benefit from the improved performance of the LHC, ALICE will upgrade several of its key detector systems including the Fast Interaction Trigger (FIT) [2]. FIT is designed to provide the functionality of the old forward detectors while retaining or even improving their performance. It will provide Minimum Bias trigger with efficiency higher than 90% for pp collisions, measure luminosity for pp and Pb-Pb, sustain interaction rates up to 1MHz and 50kHz, respectively. FIT will determine the collision time with a resolution better than 50ps, and will be used to measure the event multiplicity, the centrality and the reaction plane. The detector consists of 2 arrays of Cherenkov radiators with MCP-PMT sensors, placed on both sides of the interaction point and of a single large-diameter scintillator ring. This presentation will discuss the main design concepts, detector construction, beam test results, MC simulations, and the results of detector performance studies.