Electromagnetic Calorimeter (ATLAS)

Electromagnetic Calorimeter (ATLAS)
Name	Electromagnetic Calorimeter (ATLAS)
Location	CERN
Detector	ATLAS experiment
Collider	Large Hadron Collider
Type	Calorimeter
Technology	Liquid argon
Commissioning	2008
Status	Operational

Electromagnetic Calorimeter (ATLAS) The Electromagnetic Calorimeter in the ATLAS experiment is a precision particle detector subsystem designed to measure the energy and position of electrons and photons produced in collisions at the Large Hadron Collider in CERN. It plays a central role in searches undertaken by collaborations such as ATLAS Collaboration for signals like the Higgs boson, decays studied by teams including those from Imperial College London and University of Chicago, and precision measurements related to results reported by institutions like Fermilab and DESY. The calorimeter's performance underpins analyses published in journals managed by publishers like Nature Publishing Group and Physical Review Letters.

Overview

The calorimeter is a sampling device using liquid argon as the active medium paired with absorber plates of lead to create electromagnetic showers initiated by particles emerging from the ATLAS interaction point. It occupies the barrel and endcap regions concentric with the ATLAS inner detector and the ATLAS muon spectrometer, interfacing with systems developed at laboratories such as Brookhaven National Laboratory and Lawrence Berkeley National Laboratory. The subsystem contributes to trigger decisions taken with hardware designed in concert with groups from University of Oxford and SLAC National Accelerator Laboratory during runs coordinated by the CERN Accelerator Complex.

Design and Construction

Design choices trace to proposals assembled by engineers and physicists linked to institutions like University of Manchester, University of Tokyo, and INFN. The calorimeter uses an accordion-shaped geometry in the barrel to ensure full azimuthal coverage, a concept refined in workshops attended by delegates from Columbia University and École Polytechnique. Construction employed cryogenic systems inspired by designs from CERN Cryogenics teams and manufacturing techniques implemented in facilities including Thales Group and GE Energy. Readout electronics were developed with contributions from National Institute for Nuclear Physics groups and semiconductor vendors collaborating with University of Freiburg. Mechanical integration required coordination with the ATLAS service caverns and installation schedules aligned to global timelines overseen by the LHC Project.

Performance and Calibration

Energy resolution and position resolution were characterized in test beams at sites such as CERN SPS and DESY Test Beam Facility, with calibration strategies influenced by analyses from Imperial College London and Università di Pisa. Calibration uses signals from radioactive sources, laser systems developed by teams including University of Liverpool, and physics processes like Z boson and J/psi decays observed in ATLAS datasets. Performance metrics feed into simulation frameworks maintained by collaborations with Geant4 development contributors and software teams at CERN IT Department, enabling agreement between data and Monte Carlo samples produced for groups like ATLAS Physics Coordination.

Operation and Data Processing

During LHC Run 1 and LHC Run 2 operations, the calorimeter provided inputs to level-1 and high-level triggers implemented by computing centers coordinated by the Worldwide LHC Computing Grid. Front-end electronics process ionization signals with shaping and digitization designed by consortia from University of Geneva and University of California, Berkeley. Data quality monitoring is carried out by shift crews drawn from member institutes including University of Michigan and Nagoya University, with calibrations applied in reconstruction chains maintained by the ATLAS Software Group. Processed datasets support analyses archived in repositories used by collaborations such as INSPIRE-HEP.

Upgrades and Maintenance

Upgrade programs for the calorimeter have been planned in the context of the High-Luminosity LHC upgrade coordinated by the CERN HL-LHC Project and involve hardware and electronics refurbishment informed by studies from University of Bonn, CEA Saclay, and University of Freiburg. Maintenance campaigns are scheduled during long shutdowns organized by the LHC Committee and carried out with logistics handled by CERN Technical Services and partner laboratories like RAL. Prototyping for new readout and cooling systems involves test facilities at SINAP and collaborations with industry partners such as CATEC.

Physics Results and Impact

The Electromagnetic Calorimeter's precision measurements of photon and electron energies were critical to the discovery of the Higgs boson and to subsequent studies of its properties published by the ATLAS Collaboration and cross-checked with results from CMS experiment. It enables searches for phenomena predicted by theories proposed at institutions like Princeton University and Massachusetts Institute of Technology, including analyses targeting signatures of supersymmetry and extra dimensions. Calibration and performance studies have informed detector designs in experiments proposed at laboratories such as KEK and J-PARC, and its technological heritage influences future projects reviewed by agencies like European Research Council and STFC.

Category:Particle detectors Category:ATLAS experiment Category:CERN