Performance of the ATLAS Liquid Argon Calorimeterafter three years of LHC operation and plans for a future upgrade

The ATLAS experiment is a multi-purpose detector built foranalyzing LHC collision data. In July 2012, ATLAS announced thediscovery of the Higgs boson, the last undiscovered particle in theStandard Model of Particle Physics. The ATLAS Liquid Argon (LAr)Calorimeter played a crucial role in the discovery by providingaccurate measurements of Higgs final state objects such as photons,electrons and jets. The LAr detector is a sampling calorimeterconsisting of four subsystems: an electromagnetic barrel,electromagnetic endcaps, hadronic endcaps, and forwardcalorimeters. The purity and temperature of the liquid argonremained well above the required levels throughout the data-takingperiod. Overall the calorimeter performed very well, with over 99%of data it collected in 2012 proton-proton collisions being suitablefor physics analyses. In order to ensure good LAr detectorperformance at future higher luminosity LHC operation, severalupgrades are being planned and implemented.