ATLAS Trigger and Data Acquisition

ATLAS Trigger and Data Acquisition
Name	ATLAS Trigger and Data Acquisition
Established	2000s
Location	CERN
Type	Subsystem
Parent	ATLAS

ATLAS Trigger and Data Acquisition is the integrated subsystem that selects and records collision events produced by the Large Hadron Collider for the ATLAS experiment at CERN. It reduces the raw interaction rate from the bunch-crossing frequency to a sustainable storage rate while interfacing with detector electronics, computing farms, and offline Worldwide LHC Computing Grid tiers. The system evolved through commissioning phases associated with LHC startup, major maintenance periods, and upgrades coordinated with collaborations across European Organization for Nuclear Research projects.

Overview

The subsystem resides at the intersection of detector front-end electronics, high-throughput networking, and large-scale computing infrastructure, drawing on expertise from collaborations tied to University of Oxford, University of Chicago, Lawrence Berkeley National Laboratory, Max Planck Society, and national laboratories such as Brookhaven National Laboratory. It supports physics goals including measurements connected to Higgs boson, searches for supersymmetry, and studies of quantum chromodynamics signatures, while operating within constraints set by the LHC Run 1, LHC Run 2, and High-Luminosity LHC eras. Coordination involves governance from bodies like the ATLAS Collaboration management boards and technical coordination committees that liaise with projects such as CERN OpenLab.

System Architecture

The architecture integrates front-end modules linked to subdetectors including the Inner Detector, ATLAS Calorimeter, Muon Spectrometer, and timing layers. Data flows through optical links to the readout electronics and is staged by systems designed by teams at institutions such as University of Manchester, University of Tokyo, and Institut National de Physique Nucléaire et de Physique des Particules. Central components include custom FPGA farms, commercial switches used by vendors like Cisco Systems and Arista Networks, and computing clusters running middleware developed with contributions from European Grid Infrastructure partners. Control and configuration employ standard interfaces defined in collaboration with CERN IT and monitored using tools influenced by Nagios-style practices and software from groups like ATLAS TDAQ developers.

Trigger System

The trigger chain comprises a multi-level selection strategy historically partitioned into hardware-level and software-level stages. The first-stage hardware trigger, informed by designs at laboratories such as CERN, SLAC National Accelerator Laboratory, and Rutherford Appleton Laboratory, evaluates coarse information from calorimeters and muon chambers; later-stage software triggers execute on processor farms sourced from partners including Fermilab and RAL. Algorithms prioritize signatures associated with W boson decays, top quark production, and exotic resonances, employing pattern recognition methods vetted against datasets produced during runs tied to Test Beam campaigns and simulated with tools like Geant4 and Pythia. Trigger menus are prepared by physics and performance groups within the ATLAS Collaboration and adjusted in response to luminosity conditions measured by instrumentation developed with LHCb and CMS collaborations.

Data Acquisition and Readout

Readout systems collect event fragments from front-end electronics and assemble complete events for selected triggers. The event-building network connects readout buffers to high-performance event filter nodes deployed across computing centers including CERN Data Centre racks and regional facilities at universities such as University of Melbourne and University of Toronto. Storage and transfer rely on protocols and services coordinated with Tier-0 and Tier-1 centers of the Worldwide LHC Computing Grid, with archival workflows interfacing with teams from Deutsches Elektronen-Synchrotron and National Institute for Nuclear Physics (Italy). Monitoring of data integrity uses checksum strategies and error reporting mechanisms developed with hardware groups and software teams from ATLAS Detector Control System collaborations.

Performance and Commissioning

Commissioning campaigns ran in concert with accelerator milestones like the initial LHC beam commissioning and subsequent intensity ramp-ups. Performance metrics—latency, throughput, and selection efficiency—were validated using cosmic-ray runs and low-luminosity collisions, with results reviewed by groups including the Physics Performance Group and the Trigger and Data Acquisition Board. Studies compared trigger efficiencies against benchmark signals such as Z boson decays and calibrations using minimum bias samples. Fault-tolerance and redundancy schemes were tested in integration exercises involving institutions such as CERN technical teams and external testbeds maintained by European Grid Infrastructure collaborators.

Upgrades and Future Developments

Planned upgrades align with the High-Luminosity LHC schedule and include enhanced hardware triggers, increased use of field-programmable gate arrays supplied by vendors collaborating with CERN Electronics Group, and expanded real-time processing using accelerators driven by partnerships with the European Processor Initiative and industry players such as Intel and NVIDIA. Long-term developments consider tighter integration with timing detectors deployed by groups including Uppsala University and University of Wisconsin–Madison, and evolution of software frameworks to leverage containerization and orchestration technologies advocated by CERN IT and cloud research projects.

Operational Procedures and Data Quality Monitoring

Operational protocols are codified by shift crews and coordination teams representing institutions like Columbia University, University of Melbourne, and University of Heidelberg, with run control interfaces derived from frameworks used across particle physics experiments. Data quality monitoring pipelines produce prompt feedback on detector and trigger performance for physics groups such as those studying electroweak interactions and rare processes, while summary histograms and alarms are reviewed by experts from national labs including Fermilab and DESY. Continuous improvement cycles integrate lessons from incident reviews, hardware maintenance coordinated with CERN Engineering departments, and software updates validated by commissioning teams.

Category:ATLAS