Abstract

The Level-1 Calorimeter Trigger is a major part of the first stage of event selection for the ATLAS experiment at the LHC. It is a digital, pipelined system with several stages of processing, largely based on FPGAs, which perform programmable algorithms in parallel with a fixed latency to process about 300 Gbyte/s of input data. The real-time output consists of counts of different types of trigger objects and energy sums. Prototypes of all module types have been undergoing intensive testing before final production during 2005. Verification of their correct operation has been performed stand-alone and in the ATLAS test-beam at CERN. Results from these investigations will be presented, along with a description of the methodology used to perform the tests.

Highlights

  • The ATLAS Level-1 trigger has to provide a decision within a fixed time of 2 μs in order to reduce the LHC bunch-crossing rate of 40 MHz down to a rate of less than 75 kHz of events to be retained for the second level of event selection

  • The algorithms used have to be simple enough to be performed over a large number of input signals in this limited time, but sophisticated and flexible enough to distinguish potentially interesting particle signatures from a large and, to some extent, unpredictable background. These requirements have necessitated a design which incorporates several layers of processing being performed in parallel, with all algorithms implemented in FPGAs to allow flexibility

  • The real-time output of the trigger system consists of counts of electron/photon-like, tau-like, or jet-like clusters above programmable transverse energy thresholds, as well as results of threshold comparisons on missing and total transverse energy to be sent to the Central Trigger Processor (CTP)

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Summary

16 June 2005

Abstract- The Level-1 Calorimeter Trigger is a major part of the first stage of event selection for the ATLAS experiment at the LHC. It is a digital, pipelined system with several stages of processing, largely based on FPGAs, which perform programmable algorithms in parallel with a fixed latency to process about 300 Gbyte/s of input data. Prototypes of all module types have been undergoing intensive testing before final production during 2005 Verification of their correct operation has been performed stand-alone and in the ATLAS test-beam at CERN. Results from these investigations will be presented, along with a description of the methodology used to perform the tests

INTRODUCTION
THE ATLAS LEVEL-1 CALORIMETER TRIGGER ARCHITECTURE
GENERIC MODULE DESIGN AND CHALLENGES
LABORATORY TESTING METHODOLOGY
Simulation Software
Artificial Trigger Generation
Signal Strobing Timing Windows
Detector Correlations
Internal Consistency Checks of Trigger Data
CONCLUSION
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