ATLAS Liquid Argon Calorimeter
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| ATLAS Liquid Argon Calorimeter | |
|---|---|
| Name | ATLAS Liquid Argon Calorimeter |
| Location | CERN, Meyrin |
| Type | Particle detector subsystem |
| Established | 1990s |
| Owner | CERN |
| Operator | ATLAS experiment |
ATLAS Liquid Argon Calorimeter The ATLAS Liquid Argon Calorimeter is a key ATLAS experiment detector subsystem located at CERN designed to measure electromagnetic and hadronic energy using liquid argon as the active medium. It provides high-precision measurements used in major analyses by collaborations associated with Large Hadron Collider, enabling discoveries such as those reported in Higgs boson searches and precision studies tied to Standard Model tests. The calorimeter interfaces with global systems developed in coordination with institutions including University of Oxford, Brookhaven National Laboratory, and University of Chicago.
Overview
The device is part of the ATLAS experiment inner-to-outer detector suite alongside the ATLAS tile calorimeter, ATLAS muon spectrometer, and ATLAS inner detector. Designed during the Large Hadron Collider construction era, it serves both the ATLAS Trigger System and offline reconstruction chains used by collaborations from institutes like Imperial College London and University of California, Berkeley. The subsystem contributes to event selections employed in datasets recorded during Run 1 (LHC), Run 2 (LHC), and Run 3 (LHC), and its performance factors into searches for phenomena explored in analyses affiliated with ATLASPublicResults teams.
Design and Components
The calorimeter uses accordion-shaped electrodes immersed in cryogenic liquid argon housed within cryostats assembled at CERN with contributions from LAPP (Laboratoire d'Annecy-le-Vieux de Physique des Particules), INFN, and other partner laboratories. Its principal modules include the electromagnetic barrel and endcap calorimeters, forward calorimeters, and presampler systems developed in collaboration with groups from University of Manchester, Ludwig Maximilian University of Munich, and University of Tokyo. Mechanical support structures and cryogenics integrate technologies from European Organization for Nuclear Research engineering groups and follow designs influenced by earlier detectors such as UA1 experiment and CMS Electromagnetic Calorimeter projects. Readout segmentation, absorber materials, and high-voltage systems were specified by working groups including teams from Argonne National Laboratory and KEK.
Operation and Readout Electronics
Signal collection is performed by electrode arrays producing ionization pulses in liquid argon that are amplified and shaped by front-end electronics developed with partners like CERN EP groups, STFC, and industrial suppliers. The readout chain includes analog preamplifiers, shapers, and digitizers feeding into back-end systems integrated with the ATLAS Trigger System and TDAQ infrastructure. Time, amplitude, and pulse-shape measurements are synchronized using timing systems coordinated with LHC Clock distribution, and monitored by software frameworks related to Athena (software), Gaudi (software), and data-quality teams from participating universities. The electronics design addresses constraints from cooling systems maintained by CERN Cryogenics teams and interfaces with cabling and power-management solutions used at Point 1 (LHC).
Calibration and Performance
Calibration employs multiple techniques including charge injection systems, radioactive sources, laser systems, and physics-process calibration using electrons from Z boson decays and photons from pi0 and J/psi processes. Dedicated calibration teams from institutions like CERN, University of Liverpool, and LAPP maintain procedures and databases integrated with analysis workflows in ROOT (software) and Athena (software). Performance metrics such as energy resolution, linearity, and uniformity are evaluated in test-beam campaigns at facilities including CERN Proton Synchrotron and compared to simulations using GEANT4 and reconstruction algorithms developed by the ATLAS Collaboration.
Radiation Effects and Mitigation
The calorimeter endures radiation fields arising from collisions in the Large Hadron Collider and from activation near Point 1 (LHC). Radiation-hard electronics strategies and material choices were informed by studies at CERN Radiation Protection groups, with mitigation measures implemented in coordination with ATLAS Upgrade projects and radiation-monitoring systems. Forward regions employ designs influenced by work at European XFEL and experience from LHCb and CMS subsystems to limit gain loss, leakage current increase, and signal degradation over operational runs. Long-term plans align with High-Luminosity Large Hadron Collider upgrade roadmaps developed by the CERN Council and partner laboratories.
Integration with ATLAS Detector
Mechanically and electronically integrated into the ATLAS experiment infrastructure, the calorimeter interfaces with the ATLAS magnet system, Inner Detector (ATLAS), and offline computing grids such as the Worldwide LHC Computing Grid. Installation and maintenance operations involve coordination with detector operations teams at CERN and institutes across the ATLAS Collaboration, with safety, alignment, and service routing overseen during shutdowns defined by Long Shutdown 1 (LHC) and Long Shutdown 2 (LHC). Data from the calorimeter feed into central reconstruction chains used in analyses with authors from institutions including University of Melbourne, University of São Paulo, and University of Toronto.
Historical Development and Upgrades
Design and construction spanned collaborations formed in the 1990s and 2000s with contributions from national laboratories such as Brookhaven National Laboratory, Fermilab, and European universities including Université Paris-Sud. After commissioning during the LHC start-up, the calorimeter underwent performance tuning and firmware upgrades in synchronization with Run 1 (LHC) and Run 2 (LHC). Upgrade efforts for the High-Luminosity Large Hadron Collider era involve front-end electronics replacements, improved cooling, and enhanced radiation tolerance guided by working groups within the ATLAS Collaboration and coordinated with agencies like STFC and INFN.