Abstract
The ATLAS Level-1 Central Trigger (L1CT) system is a central part of ATLAS data-taking and has undergone a major upgrade for Run 2 of the LHC, in order to cope with the expected increase of instantaneous luminosity of a factor of two with respect to Run 1. The upgraded hardware offers more flexibility in the trigger decisions due to the factor of two increase in the number of trigger inputs and usable trigger channels. It also provides an interface to the new topological trigger system. Operationally - particularly useful for commissioning, calibration and test runs - it allows concurrent running of up to three different subdetector combinations. An overview of the operational software framework of the L1CT system with particular emphasis on the configuration, controls and monitoring aspects is given. The software framework allows a consistent configuration with respect to the ATLAS experiment and the LHC machine, upstream and downstream trigger processors, and the data acquisition system. Trigger and dead-time rates are monitored coherently at all stages of processing and are logged by the online computing system for physics analysis, data quality assurance and operational debugging. In addition, the synchronisation of trigger inputs is watched based on bunch-by-bunch trigger information. Several software tools allow for efficient display of the relevant information in the control room in a way useful for shifters and experts. The design of the framework aims at reliability, flexibility, and robustness of the system and takes into account the operational experience gained during Run 1. The Level-1 Central Trigger was successfully operated with high efficiency during the cosmic-ray, beam-splash and first Run 2 data taking with the full ATLAS detector.
Highlights
The Large Hadron Collider (LHC) [1] at CERN is a 27 km proton√–proton collider with a maximum design collision energy of s = 14 TeV
Using the information from all subdetectors in regions where high-pT activity has been previously detected by the Level-1 Trigger (“Regions of Interest”) or the full event information, the High-Level Trigger (HLT) [4] reduces the rate to a permanently recorded rate of up to 1 kHz
While the Level-1 trigger is implemented in custom-built hardware and operated synchronously to the LHC bunch crossing, the High-Level Trigger uses software-based trigger algorithms which are run on a dedicated farm of computers
Summary
This content has been downloaded from IOPscience. Please scroll down to see the full text. Ser. 664 082013 (http://iopscience.iop.org/1742-6596/664/8/082013) View the table of contents for this issue, or go to the journal homepage for more. Download details: IP Address: 137.138.124.206 This content was downloaded on 24/02/2016 at 13:13 Please note that terms and conditions apply. 21st International Conference on Computing in High Energy and Nuclear Physics (CHEP2015) IOP Publishing. Journal of Physics: Conference Series 664 (2015) 082013 doi:10.1088/1742-6596/664/8/082013
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