ATLAS (particle detector)

ATLAS (particle detector)
Name	ATLAS
Location	CERN, Meyrin, Switzerland
Type	Particle detector
Established	2008

ATLAS (particle detector) ATLAS is a general-purpose particle detector at the Large Hadron Collider facility of CERN near Geneva. Designed to investigate a wide range of fundamental questions in particle physics, ATLAS records proton–proton, proton–lead, and lead–lead collisions produced by the Large Hadron Collider to study phenomena predicted by the Standard Model (physics), search for physics beyond the Standard Model (physics), and probe properties of the Higgs boson and heavy flavor physics. The experiment involves an extensive multinational collaboration linking institutions such as University of Oxford, Brookhaven National Laboratory, and Lawrence Berkeley National Laboratory and participates in joint efforts with experiments like CMS and LHCb.

Overview

ATLAS operates as one of the two large general-purpose detectors alongside CMS at the Large Hadron Collider, with complementary designs enabling cross-checks of major discoveries such as the 2012 observation of a Higgs-like particle reported concurrently by ATLAS and CMS. The detector records data from collisions delivered by Large Hadron Collider runs, contributing to measurements related to electroweak symmetry breaking, top quark physics, quantum chromodynamics investigated at Fermilab experiments, and searches relevant to theories like supersymmetry and extra dimensions. ATLAS's scientific program is integrated with global efforts at facilities such as KEK and DESY, and its results are presented at conferences like the International Conference on High Energy Physics.

Design and Components

ATLAS features a layered design combining multiple subsystems: an inner tracking detector, calorimeters, a muon spectrometer, and magnet systems. The inner detector uses silicon pixel detectors and silicon microstrip trackers patterned after technology developed at Stanford Linear Accelerator Center projects and SLAC National Accelerator Laboratory initiatives, complemented by a transition radiation tracker concept related to developments at Imperial College London. Electromagnetic calorimetry is provided by a liquid-argon system with cryogenics expertise akin to systems at Fermilab cryogenics programs, while hadronic calorimetry uses a combination of scintillator-tile modules and sampling techniques developed with partners including Daresbury Laboratory. A toroidal magnet system, engineered with contributions from CERN member states and industrial partners, envelops the muon spectrometer where precision chambers such as monitored drift tubes and cathode strip chambers—technologies also used in experiments at DESY—measure muon trajectories. Trigger and data acquisition electronics were developed in coordination with institutes like INFN and CEA, implementing multi-level triggers inspired by earlier experiments at CERN SPS and LEP.

Performance and Data Acquisition

ATLAS's multi-tiered trigger system reduces collision rates from the LHC bunch crossing frequency to manageable storage rates, employing a hardware first-level trigger and a high-level software trigger developed with contributions from University of California, Berkeley and ETH Zurich. Data acquisition is distributed across computing grids coordinated with the Worldwide LHC Computing Grid and national centers including GridPP and NERSC, using storage models influenced by practices at SLAC and Fermilab. Detector performance metrics—momentum resolution, jet energy scale, b-tagging efficiency, and missing transverse energy resolution—are continually validated against standards from experiments like Tevatron detectors at Fermilab and tuned using Monte Carlo tools such as those developed at CERN theory groups and DESY computing groups. Upgrades for higher-luminosity running incorporate technologies tested at institutions like KEK and INFN to maintain performance in harsher radiation environments.

Physics Program and Discoveries

ATLAS's physics program spans precision measurements and searches: precision top quark mass and cross-section determinations leveraging analyses shared with CDF and D0 communities; electroweak measurements that scrutinize predictions from Quantum Chromodynamics groups at CERN; and searches for new phenomena, including resonances motivated by models from Pierre Ramond-inspired theories and frameworks such as supersymmetry explored by groups at University of Cambridge. The landmark 2012 observation of a Higgs-like boson involved ATLAS and CMS analyses confirming a particle consistent with predictions from Peter Higgs and contemporaries; subsequent ATLAS measurements of couplings, spin-parity, and rare decays engage collaborations with theorists from Princeton University and Massachusetts Institute of Technology. ATLAS also studies heavy-ion collisions to investigate quark–gluon plasma phenomena in synergy with findings from RHIC at Brookhaven National Laboratory and complements flavor physics results from LHCb.

Construction and Commissioning

Construction of ATLAS was a large-scale international engineering project managed by CERN with major contributions from national funding agencies such as STFC (United Kingdom), DOE (United States), and INFN (Italy). Key components were fabricated at institutions including KEK, CEA Saclay, Max Planck Institute for Physics, and delivered to the CERN Meyrin site for assembly in the Cavern housing the Large Hadron Collider detectors. Commissioning phases involved integration tests, beam-halo studies during LHC injection tests, and cosmic-ray runs coordinated with groups from University of Tokyo and University of Melbourne to align subsystems and validate calibration constants. The first proton–proton collisions recorded in 2009–2010 established baseline performance metrics prior to the 2012 Higgs-era analyses.

Collaboration and Organization

The ATLAS Collaboration is governed by institutional boards and an elected spokesperson drawn from member institutions such as University of Oxford, University of Chicago, and CERN. The collaboration comprises universities and laboratories across Europe, the Americas, Asia, Africa, and Oceania, with management structures mirroring those used by large collaborations at Fermilab and KEK. Working groups span detector subsystems, physics analysis, software, computing, and upgrade projects, coordinated through plenary meetings at venues like CERN and conference series such as the International Conference on High Energy Physics. Funding and oversight involve agencies including European Commission research frameworks and national science ministries associated with participating institutions.

Category:Particle detectors Category:CERN experiments