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The ATLAS detector at CERN's Large Hadron Collider (LHC) will be exposed to proton-proton collisions from beams crossing at 40 MHz. At the design luminosity of 10^34 cm^-2 s^-1 there are on average 23 collisions per bunch crossing. A three-level trigger system will select potentially interesting events in order to reduce the read-out rate to about 200 Hz. The first trigger level is implemented in custom-built electronics and makes an initial fast selection based on detector data of coarse granularity. It has to reduce the rate by a factor of 10^4 to less than 100 kHz. The other two consecutive trigger levels are in software and run on PC farms. We present an overview of the first-level trigger system and report on the current installation status. Moreover, we show analysis results of cosmic-ray data recorded in situ at the ATLAS experimental site with final or close-to-final hardware., Contribution to the 11th Vienna Conference on Instrumentation (2007), 12 pages, 6 figures, accepted for publication in the proceedings in NIM A

ATLAS is a detector at CERN's Large Hadron Collider where bunches of protons in counter-rotating beams will cross every 25 ns producing, on average, about 25 collisions for a total interaction rate of 1 GHz. A three-level trigger system selects bunch crossings potentially containing interesting processes. The Level-1 trigger, implemented in electronics and firmware, makes an initial selection in under 2.5 mus with an output rate of less than 100 kHz. A key element of this is the core module of the Central Trigger Processor which combines trigger information from the calorimeter and muon trigger processors to make the final Level-1 accept decision in under 75 ns. The event-selection algorithm used by the core module is based on lists of selection criteria, i.e., trigger menus, and is implemented in fully programmable look-up tables and content-addressable memories. In addition to the event selection, the core module generates dead-time in order to limit the frequency of Level-1 accepts to a rate that the sub-detector front-end electronics can support. The core module further provides trigger-summary information to the Level-2 trigger and to the data acquisition system. The design of the core module is presented, and results from recent laboratory tests and from tests with the calorimeter and muon trigger processors connected to detectors in a particle beam are shown

The ATLAS detector at CERN's Large Hadron Collider (LHC) will be exposed to proton-proton collisions from beams crossing at 40 MHz. A three-level trigger system will select potentially interesting events in order to reduce the readout rate to about 200 Hz. The first trigger level is implemented in custom-built electronics and makes an initial fast selection based on detector data of coarse granularity. It has to reduce the rate by a factor of 104 to less than 100 kHz. The other two consecutive trigger levels are in software and run on PC farms. We present an overview of the first-level central trigger and the muon barrel trigger system and report on the current installation status. Moreover, we show analysis results of cosmic-ray data recorded in situ at the ATLAS experimental site with final or close-to-final hardware.

The detector at CERN's large hadron collider (LHC) was exposed to proton-proton collisions from beams crossing at 40 MHz. A three-level trigger system will select potentially interesting events in order to reduce this rate to 100- 200 Hz. A trigger decision is made by the Level-1 central trigger processor (CTP) reducing the incoming rate to less than 100 kHz. The Level-1 decision is based on calorimeter information and hits in dedicated muon trigger detectors. The final Level-1 trigger system is currently being installed in the experiment with completion expected in autumn 2007. Cosmic ray data are regularly recorded as an increasing fraction of the trigger system comes online. We present an overview of the Level-1 trigger system architecture and report on the installation and commissioning process at the ATLAS experimental site. Emphasis is put on the integration of the CTP with the calorimeter and muon trigger systems. We show results from analyses of cosmic ray data recorded in situ and verify, where possible, that the Level-1 trigger meets the requirements and will be ready for data taking.

Due to the huge interaction rates and the tough experimental environment of pp collisions at a centre-of-mass energy sqrt(s)=14 TeV and luminosities of up to 10^34cm^-2s^-1, one of the experimental challenges at the LHC is the triggering of interesting events. In the ATLAS experiment a three-level trigger system is foreseen for this purpose. The first-level trigger is implemented in custom hardware and has been designed to reduce the data rate from the initial bunch-crossing rate of 40MHz to around 75 kHz. Its event selection is based on information from the calorimeters and dedicated muon detectors. This article gives an overview over the full first-level trigger system including the Calorimeter Trigger, the Muon Trigger and the Central Trigger Processor. In addition, recent results are reported that have been obtained from test-beam studies performed at CERN where the full first-level trigger chain was established successfully for the first time and used to trigger the read-out of up to nine ATLAS sub-detector systems. Due to the huge interaction rates and the tough experimental environment of pp collisions at a centre-of-mass energy sqrt(s)=14TeV and luminosities of up to 10^34 cm^-2 s^-1, one of the experimental challenges at the LHC is the triggering of interesting events. In the ATLAS experiment a three-level trigger system is foreseen for this purpose. The first-level trigger is implemented in custom hardware and has been designed to reduce the data rate from the initial bunch-crossing rate of 40 MHz to around 75 kHz. Its event selection is based on information from the calorimeters and dedicated muon detectors. This article gives an overview over the full first-level trigger system including the Calorimeter Trigger, the Muon Trigger and the Central Trigger Processor. In addition, recent results are reported that have been obtained from test-beam studies performed at CERN where the full first-level trigger chain was established successfully for the first time and used to trigger the read-out of up to nine ATLAS sub-detector systems. Due to the huge interaction rates and the tough experimental environment of pp collisions at a centre-of-mass energy sqrt(s)=14TeV and luminosities of up to 10^34 cm^-2 s^-1, one of the experimental challenges at the LHC is the triggering of interesting events. In the ATLAS experiment a three-level trigger system is foreseen for this purpose. The first-level trigger is implemented in custom hardware and has been designed to reduce the data rate from the initial bunch-crossing rate of 40 MHz to around 75 kHz. Its event selection is based on information from the calorimeters and dedicated muon detectors. This article gives an overview over the full first-level trigger system including the Calorimeter Trigger, the Muon Trigger and the Central Trigger Processor. In addition, recent results are reported that have been obtained from test-beam studies performed at CERN where the full first-level trigger chain was established successfully for the first time and used to trigger the read-out of up to nine ATLAS sub-detector systems. Due to the huge interaction rates and the tough experimental environment of pp collisions at a centre-of-mass energy sqrt(s)=14TeV and luminosities of up to 10^34 cm^-2 s^-1, one of the experimental challenges at the LHC is the triggering of interesting events. In the ATLAS experiment a three-level trigger system is foreseen for this purpose. The first-level trigger is implemented in custom hardware and has been designed to reduce the data rate from the initial bunch-crossing rate of 40 MHz to around 75 kHz. Its event selection is based on information from the calorimeters and dedicated muon detectors. This article gives an overview over the full first-level trigger system including the Calorimeter Trigger, the Muon Trigger and the Central Trigger Processor. In addition, recent results are reported that have been obtained from test-beam studies performed at CERN where the full first-level trigger chain was established successfully for the first time and used to trigger the read-out of up to nine ATLAS sub-detector systems. Due to the huge interaction rates and the tough experimental environment of pp collisions at a centre-of-mass energy sqrt(s)=14TeV and luminosities of up to 10^34 cm^-2 s^-1, one of the experimental challenges at the LHC is the triggering of interesting events. In the ATLAS experiment a three-level trigger system is foreseen for this purpose. The first-level trigger is implemented in custom hardware and has been designed to reduce the data rate from the initial bunch-crossing rate of 40 MHz to around 75 kHz. Its event selection is based on information from the calorimeters and dedicated muon detectors. This article gives an overview over the full first-level trigger system including the Calorimeter Trigger, the Muon Trigger and the Central Trigger Processor. In addition, recent results are reported that have been obtained from test-beam studies performed at CERN where the full first-level trigger chain was established successfully for the first time and used to trigger the read-out of up to nine ATLAS sub-detector systems.

The ATLAS detector at CERN's LHC will be exposed to proton-proton collisions at a bunch-crossing rate of 40 MHz. In order to reduce the data rate, a three-level trigger system selects potentially interesting physics processes. The first trigger level is implemented in electronics and firmware. It aims at reducing the output rate to less than 100 kHz. The central trigger processor (CTP) combines information from the calorimeter and muon trigger processors and makes the final Level-1-Accept (L1A) decision. It is a central element in the timing setup of the experiment. Three aspects are considered in this article: the timing setup with respect to the Level-1 trigger, with respect to the experiment, and with respect to the world. Trigger signals from the muon and calorimeter trigger processors have to be synchronized in phase with respect to the local clock, and aligned in terms of the bunch crossing they originate from. The Level-1 latency is defined as the time between the collision and the arrival of the L1A at the sub-detectors. It is fixed and less than 2.5 musec. During this time, the data from all sub-detectors are stored in front-end pipeline buffers. In order to guarantee read-out of the same collision, the pipeline lengths must be carefully tuned in order to match the Level-1 latency using several strategies with and without particle beam. The CTP further calculates a UTC time stamp derived from a GPS-based time-stamping system with a stability of 5 nsec and high absolute time precision. The time stamp will allow us to correlate ATLAS events with those in other particle-physics or astronomic detectors at CERN or elsewhere

ATLAS is a detector at CERN's Large Hadron Collider where bunches of protons in counter-rotating beams will cross every 25 ns producing, on average, about 25 collisions for a total interaction rate of 1 GHz. A three-level trigger system selects bunch crossings potentially containing interesting processes. The level-1 trigger, implemented in electronics and firmware, makes an initial selection in under 2.5 /spl mu/s with an output rate of less than 100 kHz. A key element of this is the core module of the central trigger processor which combines trigger information from the calorimeter and muon trigger processors to make the final level-1 accept decision in under 75 ns. The event-selection algorithm used by the core module is based on lists of selection criteria (trigger menu) and is implemented in fully programmable look-up tables and content-addressable memories. In addition to the event selection, the core module generates dead-time in order to limit the frequency of level-1 accepts to a rate that the sub-detector front-end electronics can support. The core module further provides trigger-summary information to the level-2 trigger and to the data acquisition system. The design of the core module is presented, and results from recent laboratory tests and from tests with the calorimeter and muon trigger processors connected to detectors in a particle beam are shown.

The authors describe an optical fiber link that is used in conjunction with the CERN host interface family to connect high-performance VAXes to VMEbus or FASTBUS over distances up to 1000 m. The modular construction allows other permutations, including VAX/VAX, FASTBUS/FASTBUS, VMEbus/VMEbus, or FASTBUS/VMEbus connections, over similar distances. The link comprises two identical optical data interconnects (ODI) connected by two unidirectional multimode fibers. The ODI at each end of the link can be connected to any device conforming to the DRB32 user interface specification. The authors discuss the operation of an ODI, the testing of the optical link, and present and future ODI implementations. >