Abstract

ATLAS is one of two general-purpose detectors at the Large Hadron Collider (LHC). The ATLAS trigger system uses fast reconstruction algorithms to efficiently reject a large rate of background events and still select potentially interesting signal events with good efficiency. After a first processing level (Level 1) using custom electronics, the trigger selection is made by software running on two processor farms, containing a total of around two thousand multi-core machines. This system is known as the High Level Trigger (HLT). To reduce the network data traffic and the processing time to manageable levels, the HLT uses seeded, step-wise reconstruction, aiming at the earliest possible rejection of background events.

Highlights

  • T HE Large Hadron Collider (LHC) [1] is a high-energy, high-intensity hadron collider built to study the Standard Model (SM) and search for physics beyond the SM

  • After giving an overview of the ATLAS trigger design and its innovative features, this paper focuses on the valuable experience gained in running the trigger in the the 2009 LHC run

  • Besides understanding the track reconstruction efficiency, it is important to look at the track parameter resolution as those are used for instance for E/p selections for electrons or impact parameter selections for B-physics triggers

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Summary

INTRODUCTION

T HE LHC [1] is a high-energy, high-intensity hadron collider built to study the Standard Model (SM) and search for physics beyond the SM. ATLAS [2] is one of two generalpurpose experiments L = 1034 cm−2s−1, located at the and collision. At√design luminosity, energy, s = 14 TeV, the LHC will deliver approximately 109 collisions/s to ATLAS. A multi-level trigger system has been designed for ATLAS to select only the most interesting events for later physics analysis. T√he LHC commissioning with beams started with coll√isions at s = 900 GeV in November 2009 and collisions at s =. Petersen is with CERN (European Organization for Nuclear Research), Geneva, Switzerland been setup to facilitate this and at the same time prepare for a more stringent selection as the luminosity grows

ATLAS TRIGGER SYSTEM
COMMISSIONING OF THE HIGHER LEVEL TRIGGER
HLT PERFORMANCE STUDIES
HLT Tracking
Calorimeter-based HLT Triggers
HLT Muon Triggers
ACTIVE HLT TRIGGER SELECTION
SUMMARY AND OUTLOOK
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