Abstract

The ATLAS High Level Trigger's primary function of event selection will be accomplished with a Level-2 trigger farm and an Event Filter farm, both running software components developed in the ATLAS offline reconstruction framework. While this approach provides a unified software framework for event selection, it poses strict requirements on offline components critical for the Level-2 trigger. A Level-2 decision in ATLAS must typically he accomplished within 10 ms and with multiple event processing in concurrent threads. In order to address these constraints, prototypes have been developed that incorporate elements of the ATLAS Data Flow -, High Level Trigger -, and offline framework software. To realize a homogeneous software environment for offline components in the High Level Trigger, the Level-2 Steering Controller was developed. With electron/gamma- and muon-selection slices it has been shown that the required performance can he reached, if the offline components used are carefully designed and optimized for the application in the High Level Trigger.

Highlights

  • T HE Large Hadron Collider (LHC) currently under construction at CERN will produce -collisions with a center of mass energy ofTeV at a design luminosity of cm s

  • The authors are with THE ATLAS HIGH LEVEL TRIGGER GROUP

  • Given the required large selectivity of the ATLAS trigger and the rare nature of the most interesting physics signatures at the LHC collider, it is essential to understand the efficiencies at each step of the event selection process

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Summary

INTRODUCTION

T HE Large Hadron Collider (LHC) currently under construction at CERN will produce -collisions with a center of mass energy of. 23 interactions per bunch crossing, it requires, highly selective trigger systems to reduce the expected interactions per second to an acceptable rate of a few hundred Hz. ATLAS [1] is one of the two large general purpose experiments at the LHC and covers a widely diversified physics program [2], ranging from discovery physics to precision measurements of Standard Model parameters. Given the required large selectivity of the ATLAS trigger and the rare nature of the most interesting physics signatures at the LHC collider, it is essential to understand the efficiencies at each step of the event selection process. Sharing a large number of software components across all platforms from the trigger event selection software to the offline physics analysis and reconstruction environment helps in achieving this goal and allows for a common development and run environment

THE ATLAS TRIGGER
HIGH LEVEL TRIGGER SELECTION SOFTWARE
THE LEVEL-2 STEERING CONTROLLER
SOFTWARE DEVELOPMENT MODEL
PERFORMANCE MEASUREMENTS
EXPERIENCES
Findings
VIII. CONCLUSION
Full Text
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