S. Rieke

The ATLAS Level-1 Calorimeter Trigger

The ATLAS Level-1 Calorimeter Trigger uses reduced-granularity information from all the ATLAS calorimeters to search for high transverse-energy electrons, photons, τ leptons and jets, as well as high missing and total transverse energy. The calorimeter trigger electronics has a fixed latency of about 1 μs, using programmable custom-built digital electronics. This paper describes the Calorimeter Trigger hardware, as installed in the ATLAS electronics cavern.

Pre-production validation of the ATLAS Level-1 calorimeter trigger system

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

First data with the ATLAS Level-1 Calorimeter Trigger

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 final system consists of over 300 custom-built VME modules, of several different types. The installation at ATLAS of these modules, and the necessary infrastructure, was completed at the end of 2007. The system has since undergone intensive testing, both in standalone mode, and in conjunction with the whole of the ATLAS detector in combined running. The final steps of commissioning, and experience with running the full-scale system are presented. Results of integration tests performed with the upstream calorimeters, and downstream trigger and data-flow systems, are shown, along with an analysis of the performance of the calorimeter trigger in full ATLAS data-taking. This includes trigger operation during the cosmic muon runs from before LHC start-up, and a first look at LHC proton beam data.

Beam test of the ATLAS level-1 calorimeter trigger system

The level-1 calorimeter trigger consists of a preprocessor (PP), a cluster processor (CP), and a jet/energy-sum processor (JEP). The CP and JEP receive digitised trigger-tower data from the preprocessor and produce regions-of-interest (RoIs) and trigger multiplicities. The latter are sent in real time to the central trigger processor (CTP) where the level-1 decision is made. On receipt of a level-1 accept, readout driver modules (RODs) provide intermediate results to the data acquisition (DAQ) system for monitoring and diagnostic purposes. RoI information is sent to the RoI builder (RoIB) to help reduce the amount of data required for the level-2 trigger. The level-1 calorimeter trigger system at the test beam consisted of 1 preprocessor module, 1 cluster processor module, 1 jet/energy module and 2 common merger modules. Calorimeter energies were successfully handled throughout the chain and trigger objects sent to the CTP. Level-1 accepts were successfully produced and used to drive the readout path. Online diagnostics were made using 4 RODs. Energy histograms were plotted and the integrity of data between the different modules was checked. All ATLAS detectors in the test beam were able to build full events based on triggers delivered by the calorimeter trigger system.

Production Test Rig for the ATLAS Level-1 Calorimeter Trigger Digital Processors

R. Achenbach b , V. Andrei b , B. Bauss , B.M. Barnett . C. Bohm , J.R.A. Booth , I.P. Brawn , D.G. Charlton , C.J. Curtis , A.O. Davis , J. Edwards , E. Eisenhandler , P.J.W. Faulkner , F. Fohlisch , C. N. P. Gee , C. Geweniger , A.R. Gillman , P. Hanke , S. Hellman , A. Hidvegi , S. Hillier , E-E. Kluge , M. Landon , K. Mahboubi , G. Mahout , K. Meier , V.J.O. Perera , W.Qian , S. Rieke , F. Ruhr , D.P.C Sankey , R.J. Staley , U. Schafer , K. Schmitt , H.C. Schultz-Coulon , S. Silverstein , R. Stamen , S. Tapprogge , J.P. Thomas , T. Trefzger , D. Typaldos , P.M. Watkins , A. Watson , P. Weber , E.E. Woerhling a

Pre-production validation of the ATLAS level-1 calorimeter trigger system

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.

Analysis of the initial performance of the ATLAS level-1 calorimeter trigger

The ATLAS first-level calorimeter trigger is a hardware-based system designed to identify high-pT jets, electron/photon and tau candidates and to measure total and missing ET in the calorimeters. The installation of the full system of custom modules, crates and cables was completed in late 2007, but, even before the completion, it was being used as a trigger during ATLAS commissioning and integration. During 2008, the performance of the full system has been tuned during further commissioning and cosmic runs, leading to its use in initial LHC data taking. Results and analysis of the trigger performance in these runs will be presented.

Commissioning Experience with the ATLAS Level-1 Calorimeter Trigger System

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.

Commissioning of the Jet/Energy-sum and Cluster Processors for the ATLAS Level-1 Calorimeter Trigger System

The ATLAS first-level calorimeter trigger is a hard warebased system designed to identify high-p T jets, electron/photon and tau candidates, and to measure total and missing E T. The trigger consists of a Preprocessor system which digitises 7200 analogue inputs, and two digit al multicrate processor systems which find jets, measure en ergy sums, and identify localised energy deposits (electron/ph oton and tau candidates). In order to provide a trigger quic kly enough, the hardware is parallel and pipelined. Experience so far of the Jet/Energy-sum and Cluster Processor system production, commissioning, and integration into ATLAS will be described.

Testing and calibrating analogue inputs to the ATLAS Level-1 Calorimeter Trigger

The ATLAS Level-1 Calorimeter Trigger is a hardwarebased system which aims to identify objects with high transverse momentum within an overall latency of 2.5μs. It is composed of a PreProcessor system (PPr) which digitises 7200 analogue input channels, determines the bunch crossing of the interaction, applies a digital noise filter, and provides a fine calibration; and two subsequent digital processors. The PreProcessor system needs various channel dependent parameters to be set in order to provide digital signals which are aligned in time and have proper energy calibration. The different techniques which are used to derive these parameters are described along with the quality tests of the analogue input signals.