Abstract

The ATLAS Level-1 Calorimeter Trigger is one of the main elements of the first stage of event selection for the ATLAS experiment at the LHC. The input stage consists of a mixed analogue/digital component taking trigger sums from the ATLAS calorimeters. The trigger logic is performed in 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 physics objects and energy sums. The production of final modules started in 2006, and installation of these modules and the necessary infrastructure at ATLAS has been underway for some time, with the intention of having a full system in situ during 2007, before first collisions at the LHC. The first experiences of commissioning and running the full scale system will be presented, along with results from integration tests performed with the upstream calorimeters, and the downstream trigger and data flow systems.

Highlights

  • The ATLAS Level-1 trigger is designed to provide a trigger 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 Level-1 Calorimeter trigger system consists of several designs of module, and each of these was extensive tested on a small scale at the prototyping phase

  • The fast 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) [2]

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Summary

30 May 2007

Abstract—The ATLAS Level-1 Calorimeter Trigger is one of the main elements of the first stage of event selection for the ATLAS experiment at the LHC. The input stage consists of a mixed analogue/digital component taking trigger sums from the ATLAS calorimeters. The trigger logic is performed in 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 physics objects and energy sums. The first experiences of commissioning and running the full scale system will be presented, along with results from integration tests performed with the upstream calorimeters, and the downstream trigger and data flow systems. Index Terms — triggering, pipeline processing, real time systems, parallel architectures

INTRODUCTION
THE ATLAS LEVEL-1 CALORIMETER TRIGGER
BREAKDOWN OF THE TRIGGER SYSTEM INTO A PARALLEL
From system to subsystems
Consequence of overlapping windows
Direct and Fanout Connectivity
INSTALLATION OF THE FULL SCALE SYSTEM
FULL SCALE CRATE TESTS
Preprocessor system
Processor system
INTEGRATION WITH EXTERNAL ATLAS SYSTEMS
Region of Interest data to the ATLAS RoIB
Findings
CONCLUSION
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