ATLAS Calorimeter

ATLAS Calorimeter
Name	ATLAS Calorimeter
Location	CERN, Geneva
Experiment	ATLAS experiment
Detector type	Calorimeter
Components	Electromagnetic calorimeter; Hadronic calorimeter; Forward calorimeter
Operation	Since 2008
Collaboration	ATLAS Collaboration

ATLAS Calorimeter The ATLAS Calorimeter is a large-scale detector subsystem of the ATLAS experiment at CERN designed to measure the energy of particles produced in Large Hadron Collider collisions; it works alongside the Inner Detector, Muon Spectrometer, Trigger system, and Data Acquisition system to enable searches such as the discovery of the Higgs boson and measurements related to the Standard Model. Its performance is central to precision studies at the LHC, informing analyses by the ATLAS Collaboration, and interfacing with projects like the High-Luminosity LHC upgrade and international efforts at laboratories such as Fermilab, DESY, and KEK.

Overview

The calorimeter system comprises an Electromagnetic calorimeter based on liquid-argon technology and a hadronic calorimeter using steel-scintillator and liquid-argon modules, combining to deliver full azimuthal coverage for the ATLAS detector; it operates in concert with the LHC accelerator complex, the ATLAS trigger chains, the Worldwide LHC Computing Grid, and the CERN accelerator complex to record data for physics groups studying phenomena like Electroweak interaction, Quantum Chromodynamics, and searches for Beyond the Standard Model. The subsystem's geometry and segmentation were optimized through collaborations involving institutions such as University of Oxford, Imperial College London, Brookhaven National Laboratory, CEA Saclay, and Max Planck Institute for Physics to ensure compatibility with reconstruction algorithms developed by the ATLAS computing group, the CALICE collaboration, and simulation frameworks like GEANT4.

Design and Components

The electromagnetic section employs accordion-shaped electrodes and lead absorbers using liquid argon readout, integrating with cryostat systems developed with input from CERN Cryogenics, Brookhaven National Laboratory, CEA, LAPP Annecy and INFN teams, while the hadronic barrel uses steel-scintillator tiles crafted in coordination with University of Manchester, LAL Orsay, Iowa State University, and University of Tokyo groups; the forward calorimeters extend coverage into the forward region supporting physics studied by groups from University of Michigan, University of California, Berkeley, University of Wisconsin–Madison, and University of Melbourne. The calorimeter includes the Liquid Argon Electromagnetic Calorimeter, the Tile Calorimeter, and the Forward Calorimeter, each instrumented with thousands of channels, front-end electronics designed with partners like CERN EP-ESE, NIKHEF, and JINR Dubna, and readout boards integrated into the ATLAS readout architecture developed with contributions from RAL, SLAC, and University of Victoria.

Performance and Calibration

Calibration and performance studies are maintained through test beams at facilities such as CERN SPS, DESY test beam, Fermilab Test Beam Facility, and measurements by analysis teams from University College London, Columbia University, Lund University, and ETH Zurich employing techniques tied to the Z boson peak, isolated electrons, and single hadron responses; energy resolution, linearity, and uniformity are quantified using data-driven methods and simulation comparisons with GEANT4, tuning by software groups like Athena (software), and validation against samples used in Higgs boson and Top quark measurements. Time and spatial resolution are optimized through calibration systems developed with CERN Electronics Group, laser and radioactive source systems designed with CEA, IN2P3, and PNPI, and in situ techniques exploiting processes such as W boson decays and Z boson calibration channels used by analysis teams across the ATLAS Collaboration.

Data Acquisition and Readout

Front-end electronics digitize signals at LHC bunch-crossing rates and pass data through the ATLAS Level-1 trigger and high-level trigger chains developed by groups from CERN, University of Chicago, University of California, Santa Cruz, and TRIUMF into the ATLAS Data Acquisition framework, with buffering, zero-suppression, and shaping implemented in ASICs designed with contributions from NIKHEF, INFN CNAF, and KEK. Readout links use optical fibers and FELIX-based architectures coordinated with CERN IT, ATLAS TDAQ, Worldwide LHC Computing Grid, and regional centers such as GridPP, NDGF, and Open Science Grid for distribution to computing centers including CERN Tier-0 and international Tier-1 sites. Trigger-level object reconstruction, developed by the ATLAS trigger group, employs calorimeter clustering algorithms and calibration corrections to provide real-time inputs to searches performed by teams focused on Supersymmetry, Dark matter, and precision Electroweak measurements.

Radiation Damage and Upgrades

The calorimeter faces cumulative radiation effects monitored by radiation groups in collaboration with CERN Radiation Protection, ATLAS Upgrade, High-Luminosity LHC, RADMON experts, and institutions such as CEA, INFN, KEK, and Brookhaven National Laboratory leading irradiation tests at facilities like CERN IRRAD, TRIUMF, and JPARC. Upgrade programs include electronics replacement, optical link enhancements, and cryostat improvements planned for the HL-LHC era, coordinated with the ATLAS Upgrade consortium, component testing at CERN SPS, and design reviews involving European Organization for Nuclear Research partners and international collaborators from US Department of Energy laboratories and university groups. Mitigation strategies, prototyped by projects such as the Phase-II upgrade, incorporate radiation-hard ASICs, improved cooling systems, and revised calibration schemes developed with vendors and research groups including STFC Rutherford Appleton Laboratory, CERN EP-ESE, and LAPP.

Role in Physics Analyses

The calorimeter underpins a wide array of ATLAS measurements including precision determinations of the Higgs boson properties, searches for Supersymmetry, measurements of Top quark production, studies of Jet physics, and missing transverse energy signatures relevant to Dark matter searches; analysis groups from institutions such as University of Oxford, CERN, Lawrence Berkeley National Laboratory, University of Chicago, and Kyoto University rely on calibrated calorimeter signals combined with tracking and muon systems to reconstruct objects for publications in journals overseen by collaborations like Physical Review Letters and Journal of High Energy Physics. The subsystem's contributions are central to detector performance papers, combined measurements with the Inner Detector and Muon Spectrometer, and cross-experiment comparisons with results from CMS, LHCb, and future projects at facilities including Future Circular Collider planning groups.

Category:ATLAS detector components