CERN’s ATLAS experiment

CERN’s ATLAS experiment
Name	ATLAS
Caption	Aerial view of the ATLAS cavern and detector components
Location	CERN, Meyrin, Geneva
Type	Particle detector
Discovered	2008
Collaborators	~5,000 scientists

CERN’s ATLAS experiment is a general-purpose particle detector located at CERN near Geneva, designed to explore collisions delivered by the Large Hadron Collider in the Standard Model energy regime and beyond. Developed by an international consortium including institutions from United States, United Kingdom, France, Germany, Italy and other member states, ATLAS aims to investigate phenomena such as the Higgs boson, supersymmetry, dark matter, and extra dimensions through precision measurements and searches for new particles. The project intersects with major facilities and programs like ATLAS Experiment Collaboration, the Compact Muon Solenoid, and the LHCb experiment in the global high-energy physics landscape.

Overview

ATLAS was conceived during the 1990s in planning at CERN alongside proposals for the Large Hadron Collider and underwent construction through partnerships with national laboratories such as Brookhaven National Laboratory, Fermilab, DESY, INFN, and CEA. The detector sits in the ATLAS cavern on the LHC ring and records proton–proton, proton–lead, and lead–lead collisions produced by the LHC. ATLAS’s scientific agenda connects to landmark discoveries by experiments like CMS, with major milestones including the 2012 observation of a new boson consistent with the Higgs boson as announced jointly by ATLAS Collaboration and CMS Collaboration at the CERN Council meetings. Its program spans precision tests of the Standard Model, searches inspired by theories from Supersymmetry, extra dimensions proposals, and constraints on Dark matter candidates.

Detector Design and Components

The ATLAS detector is built from concentric subsystems: an inner detector for tracking, surrounded by calorimeters and a muon spectrometer, all enclosed within a toroidal magnet system. The Inner Detector combines silicon pixel detectors, silicon microstrip detectors, and a transition radiation tracker developed with contributions from Oxford University, LBNL, and University of Tokyo. Electromagnetic and hadronic calorimetry employs liquid argon modules and scintillating tile calorimeters with engineering input from CEA Saclay, IHEP (China), and INFN. The muon system integrates monitored drift tubes, cathode strip chambers, and resistive plate chambers in layouts coordinated with TRIUMF, KEK, and CERN workshops. Magnet systems include a central solenoid and large air-core toroids, designed with expertise from Siemens and national institutes. Infrastructure such as the ATLAS cavern cryogenics, alignment systems, and trigger electronics were realized by consortia including Rutherford Appleton Laboratory and CEA.

Physics Program and Key Results

ATLAS’s physics program targets Higgs sector measurements, electroweak processes, heavy-flavor physics, and searches for beyond-Standard-Model signatures. The joint 2012 observation of a Higgs-like boson followed analyses combining channels such as H→γγ and H→ZZ*→4ℓ analyzed alongside datasets from CMS Collaboration and global fits from groups like the Particle Data Group. Precision measurements of top-quark properties, W and Z boson cross sections, and rare decay searches leverage comparisons with theoretical calculations from Quantum Chromodynamics collaborations and phenomenology groups at CERN Theory Department and Perimeter Institute. ATLAS has published limits on supersymmetric particles constrained in parameter spaces explored by ATLAS SUSY Group and placed bounds on heavy resonances proposed by Grand Unified Theory scenarios. Heavy-ion runs have informed quark–gluon plasma studies in synergy with results from ALICE and STAR.

Data Acquisition and Computing

ATLAS’s trigger and data acquisition system reduces collision rates from 40 MHz to manageable storage rates via a hardware-based Level-1 trigger and a high-level software trigger, coordinated with computing centers across the Worldwide LHC Computing Grid and national nodes such as GridPP, OTKA, TRIUMF, and NERSC. Data processing pipelines use frameworks developed in collaboration with the HEP Software Foundation and integrate simulation tools like GEANT4 and event generators from PYTHIA and HERWIG teams. Data preservation, distributed analysis, and access are mediated by grid middleware from EGI and national research networks, enabling analyses by thousands of users at universities including MIT, University of Oxford, University of Tokyo, and University of Melbourne.

Collaborations and Organization

The ATLAS Collaboration comprises institutions across continents including United States Department of Energy labs, European national laboratories such as DESY and CEA, and universities from countries like Japan, Canada, Australia, and Brazil. Governance includes an elected spokesperson, an executive board, and physics and technical coordination bodies with ties to committees at CERN and inter-experiment liaison groups with CMS Collaboration and LHCb Collaboration. Funding and resource decisions involve agencies such as European Research Council, national science foundations, and ministries represented through Memoranda of Understanding negotiated with CERN.

Upgrades and Future Plans

Planned upgrades are driven by the High-Luminosity LHC schedule, with Phase‑I and Phase‑II interventions to enhance tracking, calorimetry, and trigger capabilities. The Insertable B-Layer and planned Inner Tracker replacements aim to improve vertex resolution and radiation hardness with contributions from CERN engineering, FNAL, and industry partners. Electronics and firmware upgrades synchronize with developments in field-programmable gate array technology and high-speed optical links developed with partners like Cisco and national labs. Physics goals for future runs include precision Higgs coupling measurements, extended searches for weakly interacting massive particles and other Beyond Standard Model signatures in higher-luminosity operation.

Outreach and Education

ATLAS engages in outreach through public visits to CERN, educational programs with schools and universities, citizen science initiatives, and multimedia produced in collaboration with the European Organization for Nuclear Research communication teams. Programs like master classes with the International Particle Physics Outreach Group and partnerships with museums such as the Science Museum, London and Cité des Sciences et de l'Industrie disseminate results and inspire collaborations with artists and educators from institutions such as Smithsonian Institution.

Category:Particle detectors