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| ATLAS barrel calorimeter | |
|---|---|
| Name | ATLAS barrel calorimeter |
| Location | CERN, Geneva |
| Experiment | ATLAS experiment |
| Detector type | Electromagnetic calorimeter |
| Construction | 1990s–2000s |
| Collaborators | CERN; University of Oxford; University College London; University of Manchester; Brookhaven National Laboratory; Lawrence Berkeley National Laboratory |
| Status | Operational (with upgrades) |
ATLAS barrel calorimeter
The ATLAS barrel calorimeter is the central electromagnetic sampling calorimeter of the ATLAS experiment at CERN, designed to measure energies of electrons and photons in the barrel region of the detector. It forms a key element of the ATLAS Large Hadron Collider apparatus, contributing to measurements that underpin results such as the discovery of the Higgs boson, precision tests of the Standard Model (particle physics), and searches for physics beyond the Standard Model (particle physics). The device interfaces with the inner tracking systems and the hadronic calorimeter, providing energy resolution and shower shape information essential for reconstructing physics objects used by collaborations such as ATLAS experiment and analyses from institutions like Imperial College London.
The barrel calorimeter occupies the central pseudorapidity region inside the ATLAS solenoid and surrounding the Inner Detector; it covers approximately |η|<1.475 and complements the endcap electromagnetic calorimeters used in forward regions. The calorimeter is a sampling device that alternates absorber and active layers to convert incident electromagnetic showers into measurable signals; it sits radially between the ATLAS Inner Detector and the Tile calorimeter, integrated into the multi-layered ATLAS calorimetry system designed during collaborations involving CERN, DESY, and national laboratories. It provides crucial input for electron, photon, and missing transverse energy reconstruction used in studies by research groups from University of California, Berkeley, Massachusetts Institute of Technology, and University of Tokyo.
The design is based on a lead–liquid argon sampling concept chosen for its radiation tolerance and stable response at cryogenic temperatures; lead absorbers create electromagnetic showers while liquid argon serves as the ionization medium. The mechanical and cryogenic design drew on expertise from institutions such as CEA Saclay, IN2P3, and Brookhaven National Laboratory, with construction phases carried out in multiple workshops across Europe and North America. Module fabrication, quality assurance, and integration involved groups from University of Liverpool, Università di Roma La Sapienza, and University of Michigan under project management coordinated at CERN. The calorimeter was installed during the detector assembly campaigns in the mid-2000s and commissioned during the initial Large Hadron Collider beam runs.
The barrel calorimeter comprises accordion-shaped electrodes and lead absorbers arranged in three longitudinal layers (front, middle, back) plus a presampler; the accordion geometry provides complete azimuthal coverage without dead regions, engineered with precision by teams from University of Oxford, Universität Mainz, and University of Freiburg. The presampler corrects for energy lost before the calorimeter entrance due to upstream material such as the ATLAS Inner Detector and the solenoid cryostat. The cryostat and cryogenic system use liquid argon at stable temperature, maintained by specialists from CERN cryogenics and industrial partners. Front-end electronics, including preamplifiers and shaping amplifiers, were developed by collaborations involving California Institute of Technology, RAL (Rutherford Appleton Laboratory), and KEK, mounted on feedthroughs connected to digitizers and readout systems.
Energy calibration combines test-beam measurements, in-situ calibration using physics processes, and electronics calibration systems; test beams at facilities like CERN SPS and collaborations with DESY provided single-particle response studies, while in-situ techniques exploit samples such as Z boson→e+e− decays and radiative W boson events. The calorimeter achieves electromagnetic energy resolution characterized by stochastic, noise, and constant terms, validated by studies from analysis groups at University College London, University of Wisconsin–Madison, and LAL (Laboratoire de l'Accélérateur Linéaire). Uniformity and stability are monitored via periodic calibration pulses and laser systems developed with contributions from Brookhaven National Laboratory and CEA Saclay, enabling long-term performance consistent with the requirements of high-precision measurements like the Higgs boson mass determination by teams across the ATLAS experiment.
During LHC operation, ionization signals in liquid argon are shaped, digitized, and transmitted to the ATLAS Data Acquisition system; the front-end electronics perform fast shaping and gain selection to handle the dynamic range required by signals from minimum-ionizing particles up to multi-TeV showers, designed by consortia including RAL (Rutherford Appleton Laboratory), LBNL (Lawrence Berkeley National Laboratory), and CEA Saclay. The readout links interface with the ATLAS Trigger and Data Acquisition system and higher-level triggers developed by computing groups at CERN and partner institutions. Robust cryogenic operations are maintained by teams coordinating with CERN operations, ensuring liquid argon purity and temperature stability critical for signal fidelity during runs of the Large Hadron Collider.
The barrel calorimeter underpins measurements involving electrons and photons central to discoveries and precision studies, contributing directly to the observation of the Higgs boson in diphoton and four-lepton channels, precision electroweak measurements such as the W boson mass, and searches for resonances and exotic signatures pursued by analysis groups at Princeton University, University of Chicago, and CERN. Its shower-shape discrimination capabilities assist in background rejection for analyses such as searches for supersymmetry by collaborations including University of Manchester and studies of heavy-ion collisions from groups like Brookhaven National Laboratory.
Upgrade programs associated with LHC luminosity increases have targeted front-end electronics, digitization rates, and radiation-hard components, coordinated by upgrade consortia involving CERN, University of Oxford, STFC Rutherford Appleton Laboratory, and international partners. Maintenance campaigns between LHC runs include cryostat inspections, electronics replacement, and calibration system enhancements, with planning connected to future runs and Phase-I/Phase-II upgrade schedules coordinated at CERN and national funding agencies. Continued detector evolution supports the ATLAS physics program and collaborations across institutions such as Imperial College London, University of Tokyo, and Lawrence Berkeley National Laboratory.
Category:ATLAS detector