ATLAS experiment

ATLAS experiment
Arpad Horvath · CC BY-SA 2.5 · source
Name	ATLAS
Caption	A cutaway diagram of the ATLAS detector.
Collaboration	ATLAS Collaboration
Accelerator	Large Hadron Collider
Location	CERN
Energy	13.6 TeV (center-of-mass)
Luminosity	~2×10³⁴ cm⁻²s⁻¹
Website	https://atlas.cern

ATLAS experiment. It is one of the two general-purpose particle detectors at the Large Hadron Collider at CERN. The collaboration involves thousands of scientists and engineers from hundreds of institutions worldwide. Its primary goals include probing the fundamental forces of nature and searching for new particles and phenomena beyond the Standard Model.

Introduction

The project was formally proposed in the early 1990s, with construction beginning later that decade. It was designed to operate at the unprecedented energy and collision rates of the Large Hadron Collider. The detector saw its first collisions in 2009, marking the start of a new era in high-energy physics. The international effort is coordinated by the ATLAS Collaboration, which includes members from institutions like the University of Oxford, the Lawrence Berkeley National Laboratory, and the Weizmann Institute of Science.

Detector

The apparatus is a cylindrical structure, approximately 45 meters long and 25 meters in diameter, surrounding one of the LHC's interaction points. It employs a layered design with several specialized sub-detector systems. The innermost tracking system, using silicon pixel detector and semiconductor tracker technologies, precisely measures charged particle trajectories. This is surrounded by a liquid-argon calorimeter for measuring electron and photon energies, and a tile calorimeter for measuring hadronic jets. An extensive muon spectrometer with monitored drift tubes and resistive plate chambers forms the outermost layer. A large solenoid magnet and a system of toroid magnets provide the magnetic fields necessary for momentum measurement.

Physics Goals

A central objective was the investigation of the mechanism of electroweak symmetry breaking, which led to the search for the Higgs boson. The program extensively tests predictions of the Standard Model and searches for physics beyond it. This includes searches for supersymmetry, extra dimensions, and candidates for dark matter. Other studies probe the properties of the top quark, investigate quantum chromodynamics, and examine the quark-gluon plasma state recreated in heavy-ion collision events.

Data Analysis

The experiment generates petabytes of data annually from billions of proton–proton collision events. A sophisticated multi-tiered trigger system filters events in real-time, reducing the data rate for permanent storage. The selected data is processed through a worldwide computing grid, the Worldwide LHC Computing Grid, for distributed analysis. Physicists use advanced statistical methods and tools like ROOT and frameworks developed within the CERN ecosystem to extract signals from background processes, often employing techniques like multivariate analysis.

Results and Discoveries

In July 2012, the collaboration, alongside the CMS experiment, announced the discovery of a new particle consistent with the Higgs boson, a milestone confirmed by subsequent precision measurements of its properties. The experiment has set stringent limits on many proposed supersymmetry models and exotic particles. It has made precise measurements of Standard Model processes, including the mass of the W boson and the top quark. Studies of heavy-ion collisions have provided insights into the properties of the quark–gluon plasma. The collaboration also participates in broader studies, such as those related to the Forward Search Experiment.

Upgrades and Future Plans

To maintain physics performance at increasing LHC luminosity, the detector has undergone a series of major upgrades. The first significant upgrade occurred during the first Long Shutdown, with improvements to the trigger and data acquisition systems. A more extensive upgrade is underway for the High-Luminosity Large Hadron Collider era, involving a completely new all-silicon inner tracker, upgraded calorimeter electronics, and a new muon system. These enhancements will allow the experiment to collect an order of magnitude more data, enabling more sensitive searches for rare processes and further precision measurements of Higgs boson couplings.

Category:Particle physics experiments Category:CERN experiments Category:Large Hadron Collider