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ATLAS (collaboration internal site, public site, ATLAS France site) is a particle physics experiment on the Large Hadron Collider at CERN, close to Geneva, Switzerland. This detector is studying proton-proton collision at unprecedented energies, in order to explore the fundamental law of physics. Data taking has started in fall 2009, and the first proton proton run was completed in fall 2012.

In 2012, ATLAS (with CMS, another CERN experiment) has reported the discovery of a new particle which is consistent to the long sought Higgs boson, the last missing piece of the Standard Model of Particle Physics. Studies are on-going to study its properties and measure their compatibilities with the expect one. Atlas is also pursuing searches concerning additional dimensions, unification of the fundamental forces, and universe dark matter candidates. All ATLAS public results are available here.

The ATLAS IJCLab group has been involved (since even before the official birth of Atlas in 1992) in the design, building, commissioning and running of the liquid argon calorimeter, which allows identification and measurement of electrons and photons. The group is also involved in the ALFA detector which allows an absolute measurement of the luminosity of the LHC. The group has also had a strong contribution in the software of the experiment in many areas.