Abstract
The ATLAS trigger successfully collected collision data during the first run of the LHC between 2009-2013 at different centre-of-mass energies between 900 GeV and 8TeV. The trigger system consists of a hardware Level-1 and a software-based high level trigger (HLT) that reduces the event rate from the design bunch-crossing rate of 40 MHz to an average recording rate of a few hundred Hz. In Run-2, the LHC will operate at centre-of-mass energies of 13 and 14 TeV and higher luminosity, resulting in up to five times higher rates of processes of interest. A brief review of the ATLAS trigger system upgrades that were implemented between Run-1 and Run-2, allowing to cope with the increased trigger rates while maintaining or even improving the efficiency to select physics processes of interest, will be given. This includes changes to the Level-1 calorimeter and muon trigger systems, the introduction of a new Level-1 topological trigger module and the merging of the previously two-level HLT system into a single event processing farm. A few examples will be shown, such as the impressive performance improvements in the HLT trigger algorithms used to identify leptons, hadrons and global event quantities like missing transverse energy. Finally, the status of the commissioning of the trigger system and its performance during the 2015 run will be presented.
Highlights
The trigger system is an essential component of the ATLAS [1] experiment at the LHC [2], since it is responsible for deciding whether or not to keep a given collision event for later study
Level-1 Trigger Upgrades Several upgrades have been introduced in the different components of the ATLAS Level-1 trigger system for Run-2 data taking
One of the main upgrades in the Level1 Calorimeter trigger is the new Multi-Chip Modules, based on field-programmable gate array (FPGA) technology, which replace the application-specific integrated circuits (ASICs) included in the modules used in Run-1
Summary
The trigger system is an essential component of the ATLAS [1] experiment at the LHC [2], since it is responsible for deciding whether or not to keep a given collision event for later study. Level-1 Trigger Upgrades Several upgrades have been introduced in the different components of the ATLAS Level-1 trigger system for Run-2 data taking The upgrades, both in the Level-1 trigger hardware and in the detector readout, allowed to rise the maximum Level-1 trigger rate from 70 kHz in Run-1 to 100 kHz in Run-2. One of the main upgrades in the Level Calorimeter trigger is the new Multi-Chip Modules (nMCM), based on field-programmable gate array (FPGA) technology, which replace the application-specific integrated circuits (ASICs) included in the modules used in Run-1. This new hardware allows the use of auto-correlation filters and a new bunch-by-bunch dynamic pedestal correction, meant to suppress pile-up effects.
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