This article on the ATLAS experiment at CERN is a guest article by Anja Sjöström, an IB diploma student from Switzerland.

The ATLAS Experiment, an acronym for A Toroidal LHC ApparatuS, is one of the four major particle physics experiments at CERN. Its detector is one of the two large general-purpose detectors situated at Interaction point 1 (one of the four high energy collision points on the Large Hadron Collider or LHC at CERN), 93 meters below ground.

Atlas Experiment CERN 2

The ATLAS detector works towards the confirmation and improvement of measurements of the Standard Model. In addition, ATLAS also contains features enabling it to search for evidence of theoretical particles that extend beyond the scope of the Standard Model. On a wider scale, the experiment as a whole mobilizes more than 3000 scientists. One of the main matters at stake is the extensive flow of data created by the interaction of the colliding proton beams when the LHC is operating. As such, a considerable part of the ATLAS experiment is to develop elaborate, precise, and accurate data digestion software that screen and sort the generated information.

Construction And Development

The ATLAS experiment traces its debuts back to 2009 when it recorded its first collision. However, the experiment and project itself hold their roots in 1992, when two collaborations combined their efforts into creating a general-purpose detector for the LHC. Proposed in its current form in 1994, budgets approved and the building of its components was undertaken all around the world with the collaboration of local industries and other institutes. Assembling began in the ATLAS experiment pit in 2003, after several years of collaboration.

Atlas Experiment CERN
Credits: CERN

Structure of ATLAS

ATLAS - The Largest Particle Detector In The World 1
The Structure Of ATLAS detector

The ATLAS detector comes in a cylindrical shape under the proportions of 46m in length and 25m in diameter, weighing 7,000 tonnes. To account for such large dimensions, ATLAS was produced around the world and assembled once the parts were lowered underground. The detector’s size is explained by its necessity to sustain high-energy collisions of the order of 6.5 TeV per proton.

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As a whole, ATLAS was built as a general-purpose detector designed to detect and measure the widest possible range of signals to detect the properties of a plethora of theoretical particles. In order to account for the detection of the thoroughly broad range of particles produced (recognized by different masses, spins, energies, lifetimes, etc.), the detector was designed in several layers around the collision point. The main components being, first of all, the inner detector surrounded by a magnetic field generated by a solenoid whose purpose is to detect charged particles and identifying their momentum (thanks to the curvature of their trajectory) as well as their charge (revealed by the direction of its track).

Beyond the inner detector are found the calorimeters which absorb and measure the energy emitted by particles and provide the main way of detecting neutral particles such as neutrons or photons. The third main layer of the detector structure is the muon spectrometer composed notably of muon chambers which measure the tracks of outgoing muons.

Atlas Experiment CERN 3
Credits: CERN

As a whole, the ATLAS detector is the largest ever built particle detector for, in addition to being designed for general purpose, having to accommodate a wide range possible tracks, the ATLAS detector had to account exorbitant rates of collisions and quantities of energy.


Back in 2012, July 12th to be exact, ATLAS was one of the two detectors which participated in the detection of the Higgs boson, which was one of ATLAS’s main goals. According to predictions and theories, the Higgs mechanism consisting of the Higgs field and its Higgs boson was said to account for the mass (inertial mass) of several elementary particles depending on how strongly a given particle would interact with the Higgs field. Being considered as the missing part of the puzzle of the Standard Model, this largely sought-after particle was known to be lower than 1 TeV, however, its practical detection remained a mystery for years having ranged beyond any of the conceivable limits imposed by existing accelerators.

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