The ATLAS Level-1 Topological Trigger performance in Run 2

Imma Riu

doi:10.1088/1742-6596/898/3/032037

Abstract

The Level-1 trigger is the first event rate reducing step in the ATLAS detector trigger system, with an output rate of up to 100 kHz and decision latency smaller than 2.5 μs. During the LHC shutdown after Run 1, the Level-1 trigger system was upgraded at hardware, firmware and software levels. In particular, a new electronics sub-system was introduced in the real-time data processing path: the Level-1 Topological trigger system. It consists of a single electronics shelf equipped with two Level-1 Topological processor blades. They receive real-time information from the Level-1 calorimeter and muon triggers, which is processed to measure angles between trigger objects, invariant masses or other kinematic variables. Complementary to other requirements, these measurements are taken into account in the final Level-1 trigger decision. The system was installed and commissioning started in 2015 and continued during 2016. As part of the commissioning, the decisions from individual algorithms were simulated and compared with the hardware response. An overview of the Level-1 Topological trigger system design, commissioning process and impact on several event selections are illustrated.

Highlights

The ATLAS experiment [1] is a general purpose detector designed to exploit the full potential of proton-proton and heavy ion collisions at the Large Hadron Collider (LHC)
The Level-1 (L1) trigger system [2] is designed to reduce the output event rate from 109 proton-proton interactions per second produced by the LHC to a maximum of 100 kHz. It is implemented in fast custom electronics designed to decide in less than 2.5 μs. It consists of three main systems: the Level-1 Calorimeter (L1Calo) trigger, the Level-1 Muon (L1Muon) trigger and the Central Trigger Processor (CTP)
The L1 Topological trigger system With the Run 1 trigger system, the L1 output rate would be kept within the maximum allowed 100 kHz by requiring higher transverse momentum pT or transverse energy ET for the L1 trigger objects. To mitigate this increase a new hardware system was introduced in the L1 trigger path: the L1 Topological (L1Topo) trigger system

Summary

Introduction

The ATLAS experiment [1] is a general purpose detector designed to exploit the full potential of proton-proton and heavy ion collisions at the Large Hadron Collider (LHC). To mitigate this increase a new hardware system was introduced in the L1 trigger path: the L1 Topological (L1Topo) trigger system It performs real-time event selection based on geometric and kinematic relationships between Trigger OBjects (TOBs), i.e. electrons/photons, muons, jets and taus, as well as on event-level quantities such as missing transverse energy. To three different categories, as detailed in table 1: angular separation between TOBs (in η, φ or radius R), invariant mass or transverse mass, and hardness of interaction (the scalar sum of pT of jets, HT) Conditions on these topological calculations are required in addition to multiplicity and a minimum pT or ET to TOBs in order to reject background events while keeping interesting ones for physics analyses.

10 ATLAS Preliminary L1Topo Commissioning

Conclusions