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The ALICE High Level Trigger comprises a large computing cluster, dedicated interfaces and software applications. It allows on-line event reconstruction of the full data stream of the ALICE experiment at up to 25 GByte/s. The commissioning campaign has passed an important phase since the startup of the Large Hadron Collider in November 2009. The system has been transferred into continuous operation with focus on the event reconstruction and first simple trigger applications. The paper reports for the first time on the achieved event reconstruction performance in the ALICE central barrel region. [ABSTRACT FROM PUBLISHER]

The present paper discusses recent advances on a Passive Optical Network inspired Timing-Trigger and Control scheme for the future upgrade of the TTC system installed in the LHC experiments' and more specifically the currently known as TTCex to TTCrx link. The timing PON is implemented with commercially available FPGAs and 1-Gigabit Ethernet PON transceivers and provides a fixed latency gigabit downlink that can carry level-1 trigger accept decisions and commands as well as an upstream link for feedback from the front-end electronics. [ABSTRACT FROM PUBLISHER]

The Data Acquisition System of the Compact Muon Solenoid experiment at the Large Hadron Collider reads out event fragments of an average size of 2 kB from around 650 detector front- ends at a rate of up to 100 kHz. The first stage of event-building is performed by the Super-Fragment Builder employing custom-built electronics and a Myrinet optical network. It reduces the number of fragments by one order of magnitude, thereby greatly decreasing the requirements for the subsequent event-assembly stage. Back-pres- sure from the down-stream event-processing or variations in the size and rate of events may give rise to buffer overflows in the subdetector's front-end electronics, which would result in data corruption and would require a time-consuming re-sync procedure to recover. The Trigger-Throttling System protects against these buffer overflows. It provides fast feedback from any of the subdetector front-ends to the trigger so that the trigger can be throttled be- fore buffers overflow. This paper reports on new performance measurements and on the recent successful integration of a scaled-down setup of the described system with the trigger and with front-ends of all major subdetectors. The ongoing commissioning of the full-scale system is discussed. [ABSTRACT FROM AUTHOR]

For the ALICE experiment at the Large Hadron Collider (LHC) at CERN/Geneva, a high level trigger system (HLT) for online event selection and data compression has been developed and a computing cluster of several hundred dual-processor nodes is being installed. A major system integration test was carried out during the commissioning of the time projection chamber (TPC), where the HLT also provides a monitoring system. All major parts like a small computing cluster, hardware input devices, the online data transportation framework, and the HLT analysis could be tested successfully. A common interface for HLT processing components has been designed to run the components from either the online or offline analysis framework without changes. The interface adapts the component to the needs of the online processing and allows the developer to use the offline framework for easy development, debugging, and benchmarking. Following this approach, results can be compared directly. For the upcoming commissioning of the whole detector, the HLT is currently prepared to run online data analysis for the main detectors, e.g., the inner tracking system (ITS), the TPC, and the transition radiation detector (TRD). The HLT processing capability is indispensable for the photon spectrometer (PHOS), where the online pulse shape analysis reduces the data volume by a factor 20. A common monitoring framework is in place and detector calibration algorithms have been ported to the HLT. The paper describes briefly the architecture of the HLT system. It focuses on typical applications and component development. [ABSTRACT FROM AUTHOR]

The ATLAS experiment at the Large Hadron Collider (LHC) will face the challenge of efficiently selecting interesting candidate events in pp collisions at 14 TeV centre-of-mass energy, whilst rejecting the enormous number of background events. The High-Level-Trigger (HLT = second level trigger and Event Filter), which is a software based trigger will need to reduce the first level trigger output rate of ∼75 kHz to ∼200 Hz written out to mass storage. In this paper an overview of the steering mechanism of the HLT is given. The HLT Steering is responsible for the schedulling of algorithms and for the global event trigger decision evaluation. The concept of step-wise and seeded selection strategy implemented by the steering will be presented. Integration of large number of trigger menus and sophisticated physics selection strategies will also be discussed. The electron and photon menus will be described to demonstrate that the trigger is well adapted for the physics program at the LHC. [ABSTRACT FROM AUTHOR]

The ATLAS experiment at the Large Hadron Collider (LHC) will face the challenge of selecting interesting candidate events in proton-proton collisions at 14 TeV center of mass energy, while rejecting the enormous number of background events. The trigger system architecture is organized in three levels. From a bunch crossing rate of 40 MHz, the First Level trigger, hardware implemented, will reduce this rate to around ∼ 75 kHz. Then the software based High Level Trigger (HLT), composed by the Second Level Trigger and the Event Filter reduces the rate to ∼ 200 Hz. In this paper, we will present the implementation of the muon trigger "slice," signal efficiencies, background rejection rates, and system performances (execution time, memory consumption, etc.) for online muon selection based on Monte Carlo simulations and results obtained on real events collected during cosmic data taking runs. [ABSTRACT FROM AUTHOR]