Status of the ATLAS Liquid Argon calorimeter and its performance after two years of LHC operation

The ATLAS detector is designed to study proton–proton collisions produced at the Large Hadron Collider (LHC) at CERN. Its calorimeter system, for the electromagnetic and forward part and for a fraction of the hadronic part, is made of liquid argon sampling calorimeters. During the 2011 data taking period, ATLAS operated with an excellent efficiency and recorded more than 5 fb − 1 integrated luminosity of 7 TeV center of mass energy proton–proton collisions. The ATLAS Liquid Argon calorimeters played a significant role in this achievement. Its main features are first described. Then, some of its performances over the past two years are given. Highlights are put on its operation, calibration, stability and data taking efficiency, as well as on the related physics performances.