The ATLAS experiment
  1. 01/10/1992

    ATLAS Collaboration publishes Letter of Intent

    The ATLAS Collaboration proposes the construction…

    Know more
  2. 15/12/1994

    Submission of Technical Proposal

    The ATLAS Collaboration submits the technical…

    Know more
  3. 01/07/1997

    Formal Approval of ATLAS Experiment

    The LHC Experiments Committee and CERN Director-…

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  4. 01/05/1998

    Excavation of the ATLAS Experiment cavern begins

    Team of engineers begin excavating a series of…

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  5. 04/06/2003

    ATLAS cavern inaugurated

    After five years of innovative and ingenious…

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  6. 20/11/2006

    World’s largest superconducting magnet turns on

    The ATLAS Barrel Toroid, a characteristic…

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  7. 04/10/2008

    End of ATLAS construction

    To celebrate the end of the ATLAS construction…

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  8. 23/11/2009

    ATLAS records first collisions

    The start of a fantastic era of physics! ATLAS…

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  9. 30/03/2010

    First LHC collisions at 7 TeV

    ATLAS records collisions at 7 TeV centre-of-mass…

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  10. 25/11/2010

    ATLAS observes striking imbalance of jet energies in heavy ion collisions

    Only 3 weeks into its first LHC heavy-ion run,…

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  11. 08/12/2010

    First ATLAS observation and rate measurement of top quark pairs

    The ATLAS Experiment observes the production of…

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  12. 04/07/2012

    ATLAS and CMS observe a particle consistent with the Higgs boson

    On 4 July 2012, as a curtain raiser to the year…

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  13. 01/02/2013

    Toward 14 Tev: preparing for increase in total energy

    In February 2013, the LHC and the ATLAS…

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  14. 10/08/2013

    Nobel Prize for the Higgs discovery

    The 2013 Nobel Prize in physics is awarded to…

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  15. 01/01/2014

    Data-taking to continue until 2035

    The LHC will be upgraded to 14 TeV collision…

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  16. 23/05/2014

    ATLAS finds evidence for the rare electroweak W±W± production

    ATLAS publishes first evidence for electroweak…

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  17. 03/06/2015

    ATLAS Begins Recording Physics Data at 13 TeV

    ATLAS began recording physics data from 13 TeV…

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  18. 07/06/2016

    Combination of Higgs boson production and decay measurements of ATLAS and CMS

    The ATLAS and CMS Experiments release combined…

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  19. 13/12/2016

    First measurement of the W boson mass at the LHC

    ATLAS shows its strength for precision physics,…

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  20. 01/04/2017

    First Technical Design Report released for ATLAS upgrade

    ATLAS begins preparations for the Phase II…

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  21. 06/06/2017

    Sighting the Higgs in its favourite decay

    ATLAS sees the first LHC evidence of the Higgs…

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  22. 14/08/2017

    First direct evidence of light-by-light scattering at high energy

    ATLAS publishes the first direct evidence of high…

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  23. 04/06/2018

    ATLAS observes direct interaction of Higgs boson with top quark

    ATLAS announces the observation of Higgs bosons…

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  24. 28/08/2018

    ATLAS observes elusive Higgs boson decay to a pair of bottom quarks

    The Higgs boson is observed decaying into a pair…

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ATLAS Collaboration publishes Letter of Intent

The ATLAS Collaboration proposes the construction of a general-purpose detector at the Large Hadron Collider. The Letter of Intent was submitted to the LHC Experiments Committee, which marked the first official use of the name ATLAS. The Letter identified a number of conceptual and technical design options, including a superconducting toroid magnet system.

Submission of Technical Proposal

ATLAS Experiment Technical Proposal and Technical Design Reports for sub-detectors. © CERN

The ATLAS Collaboration submits the technical proposal of the experiment to the LHC Experiments Committee. Approval to proceed with technical design reports would be granted in early 1996, followed by the submission of the first report on 15 December of the same year. A long series of Technical Design Reports follow.

Formal Approval of ATLAS Experiment

The LHC Experiments Committee and CERN Director-General, Chris Llewellyn Smith, approve the construction of the ATLAS detector. As the first Technical Design Reports are approved, ATLAS teams all over the world begin building detector components and worked on final technical developments.

Excavation of the ATLAS Experiment cavern begins

2000: Working inside the ATLAS cavern. © CERN

Team of engineers begin excavating a series of underground caverns in Meyrin, Switzerland. These caverns will be home to the ATLAS Experiment and its supporting infrastructure.

ATLAS cavern inaugurated

June 2003: Inauguration of ATLAS cavern. © CERN

After five years of innovative and ingenious civil engineering, the ATLAS detector cavern (35 x 55 x 40 metres) was fully excavated. ATLAS, CERN officials, and political authorities, including the President of the Swiss Confederation Pascal Couchepin, celebrated the inauguration of the first cavern on the Large Hadron Collider on 4 June 2003. Installation of the detector in the cavern began soon after.

World’s largest superconducting magnet turns on

The ATLAS detector under construction in 2005. © CERN

The ATLAS Barrel Toroid, a characteristic component of the detector, then the largest superconducting magnet ever built, is switched on for the first time. It works together with the two Endcap Toroids and a central Solenoid magnet to bend the paths of charged particles produced in collisions at the LHC, enabling important properties to be measured.

End of ATLAS construction

October 2008: Performance at the ATLAS start-up event. © CERN

To celebrate the end of the ATLAS construction phase, the Collaboration hosts a party at CERN's magnet testing facility (SM18). This was the largest ATLAS celebration yet, with collaboration members travelling from around the world to mark this milestone.

ATLAS records first collisions

The start of a fantastic era of physics! ATLAS records first collisions at 0.9 TeV.

First LHC collisions at 7 TeV

Martin Aleksa, Lyndon Evans, Fabiola Gianotti and Peter Jenni toast running at 7 TeV in the ATLAS Control Room. (IMAGE: CERN)

 

 

ATLAS records collisions at 7 TeV centre-of-mass energy for the first time. Particle physicists around the world anticipate a rich harvest of new physics as the LHC begins its first long run at an energy three and a half times higher than previously achieved at a particle accelerator. Explore the resources prepared for press.

ATLAS observes striking imbalance of jet energies in heavy ion collisions

Only 3 weeks into its first LHC heavy-ion run, ATLAS observed an unexpectedly large imbalance of energy in pairs of jets created in lead-ion collisions at the LHC. This striking effect, which is not seen in proton–proton collisions, could be a sign of strong interactions between jets and a hot, dense medium (quark-gluon plasma) formed by the colliding ions. Details studies of the effect followed this first observation.

First ATLAS observation and rate measurement of top quark pairs

The ATLAS Experiment observes the production of top quark pairs – a major milestone of the early LHC physics programme. As the heaviest known elementary particle with a strong coupling to the Higgs boson, the top quark is key to understanding physics at the energy frontier. As the LHC generates hundreds of millions of top quarks, the ATLAS Experiment is able to study the particle’s properties in great detail.

ATLAS and CMS observe a particle consistent with the Higgs boson

ATLAS spokesperson, Fabiola Gianotti, presents the collaboration's results. (IMAGE: CERN)

On 4 July 2012, as a curtain raiser to the year’s major particle physics conference, ICHEP 2012 in Melbourne, the ATLAS and CMS experiments present their latest preliminary results in the search for the long-sought Higgs particle. Both experiments have observed a new particle in the mass region around 125-126 GeV.  The next step is to determine the precise nature of the particle and its significance for our understanding of the universe. Are its properties as expected for the long-sought Higgs boson, the final missing ingredient in the Standard Model of particle physics? Or is it something more exotic? The Standard Model describes the fundamental particles from which we, and every visible thing in the universe, are made, and the forces acting between them. All the matter that we can see, however, appears to be no more than about 4% of the total. A more exotic version of the Higgs particle could be a bridge to understanding the 96% of the universe that remains obscure. Explore the resources prepared for press.

Toward 14 Tev: preparing for increase in total energy

2014: Installation of the IBL during Long Shutdown 1. © CERN

In February 2013, the LHC and the ATLAS Experiment begin the first Long Shutdown. This maintenance period would see the first upgrades to the ATLAS Experiment installed, in preparation for higher luminosity operations.

Nobel Prize for the Higgs discovery

The 2013 Nobel Prize in physics is awarded to Professors François Englert and Peter Higgs "for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider". ATLAS and CMS physicists cheered the announcement.

Data-taking to continue until 2035

The LHC will be upgraded to 14 TeV collision energy. The first major upgrade is Phase I, scheduled for 2018, and Phase 2 in 2022. The experiments will continue taking data until 2035. By then ATLAS expects to have collected 100 times more data than they had at the beginning of Long Shutdown 1.

ATLAS finds evidence for the rare electroweak W±W± production

ATLAS publishes first evidence for electroweak production of W bosons with the same charge. This channel receives contributions from quartic interactions between W bosons. This rare process gives physicists a new way to study electroweak symmetry breaking and to indirectly probe the properties of the Higgs boson.

ATLAS Begins Recording Physics Data at 13 TeV

ATLAS began recording physics data from 13 TeV proton collisions, which allow for precision studies of the Higgs boson and other Standard Model particles, as well as the search for new particles with higher masses.

Combination of Higgs boson production and decay measurements of ATLAS and CMS

The ATLAS and CMS Experiments release combined measurements of the Higgs boson production and decay rates. Examining all data from the LHC Run-1, the result gives a snapshot of the world’s knowledge of the mysterious Higgs boson. In addition to setting constraints on Higgs couplings to vector bosons and fermions, the combination established the observation of Higgs to di-tau decay and weak-boson-fusion production.

First measurement of the W boson mass at the LHC

ATLAS shows its strength for precision physics, taking a world-class measurement of the W boson mass. Precise measurements of the W boson mass are vital, as the parameter is related in the Standard Model to the masses of the top quark and the Higgs boson. Measuring the W mass can thus test the self-consistency of the Standard Model, since any deviation from the predicted relation would be a sign of new physics. This first ATLAS result is consistent and as precise as the best previous measurement of the W mass.

First Technical Design Report released for ATLAS upgrade

ATLAS begins preparations for the Phase II upgrade of the experiment, which will be in place for the High-Luminosity LHC. This upgraded ATLAS experiment will begin data taking in 2026.

Sighting the Higgs in its favourite decay

ATLAS sees the first LHC evidence of the Higgs boson decaying to a pair of b-quarks. Despite being the dominant Higgs decay, finding evidence in this channel was a major challenge. Following years of dedicated search, ATLAS was able to spot this elusive decay in 2017, with an observed significance of 3.6 σ (expectation 4.0 σ) when combining the Run 1 and Run 2 datasets.

First direct evidence of light-by-light scattering at high energy

ATLAS publishes the first direct evidence of high energy light-by-light scattering, a very rare process in which two photons – particles of light – interact and change direction. The result, published in Nature Physics, confirms one of the oldest predictions of quantum electrodynamics.

ATLAS observes direct interaction of Higgs boson with top quark

ATLAS announces the observation of Higgs bosons produced together with a top-quark pair. This rare process is one of the most sensitive tests of the Higgs mechanism and its observation marked a significant milestone for the field of High-Energy Physics.

ATLAS observes elusive Higgs boson decay to a pair of bottom quarks

The Higgs boson is observed decaying into a pair of bottom quarks for the first time. This elusive interaction is predicted to make up almost 60% of the Higgs boson decays and is thus primarily responsible for the Higgs natural width.