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The ATLAS Trigger System

Leonardo Toffolin

Abstract

The ATLAS Trigger system is a key component of the ATLAS experiment at the CERN Large Hadron Collider (LHC), designed to reduce the event rate from the 40 MHz proton-proton bunch crossing frequency to an output suitable for offline storage and analysis. During Run-3 (2022-2026), major upgrades were implemented in both the hardware-based Level-1 (L1) Trigger and the software-based High Level Trigger (HLT), to cope with increased luminosity and pile-up conditions. This paper summarises the main features of the ATLAS Trigger system, its performance in Run-3, and its role in enabling precision measurements and new physics searches.

The ATLAS Trigger System

Abstract

The ATLAS Trigger system is a key component of the ATLAS experiment at the CERN Large Hadron Collider (LHC), designed to reduce the event rate from the 40 MHz proton-proton bunch crossing frequency to an output suitable for offline storage and analysis. During Run-3 (2022-2026), major upgrades were implemented in both the hardware-based Level-1 (L1) Trigger and the software-based High Level Trigger (HLT), to cope with increased luminosity and pile-up conditions. This paper summarises the main features of the ATLAS Trigger system, its performance in Run-3, and its role in enabling precision measurements and new physics searches.
Paper Structure (8 sections, 3 figures)

This paper contains 8 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Level-1 Trigger System
  3. L1 Calorimeter Trigger
  4. L1 Muon Trigger
  5. L1Topo and CTP
  6. High Level Trigger
  7. Data streams and operations
  8. Summary and Outlook

Figures (3)

  • Figure 1: Architecture of the ATLAS Trigger system atlas_trigger2024.
  • Figure 2: Efficiency of the L1 single large-$R$ jet trigger in Run-3. The large-$R$ jet variants present a sharper turn-on and better plateau efficiency than the legacy J100 (small-$R$ jet) item l1calo_public.
  • Figure 3: (a) Efficiency of the L1 muon trigger with 2023 and 2024 Run-3 data l1muon_public. (b) Efficiency of the L1 single muon trigger in Run-3 l1muon_public.