Performance of the ATLAS liquid argon calorimeter

The Liquid Argon calorimeter (LAr) is a key detector component in the ATLAS experiment at the LHC. It provides precision measurements of electrons, photons, jets and missing transverse energy produced in the LHC proton-proton collisions. The calorimeter system consists of an electromagnetic barrel calorimeter and two electromagnetic endcaps (EMECs), hadronic (HEC) and forward (FCal) calorimeters. The lead-liquid argon sampling technique with an accordion geometry was chosen for the barrel electromagnetic calorimeter (EMB) and adapted to the electromagnetic endcaps. A presampler (PS) is installed in the cryostat in front of the EM calorimeter to provide a measurement of the energy lost upstream. The hadronic endcap calorimeter (HEC) uses a copper-liquid argon sampling technique with plate geometry. Finally, the forward calorimeter is composed of three modules featuring cylindrical electrodes with thin liquid argon gaps. The barrel and the two endcaps are housed into three cryostats kept at about 88 K. We present results assessing the liquid argon calorimeter performance obtained using random triggers, calibration data and LHC proton-proton collisions. Properties of the read-out channels such as pedestal, noise and gain have been measured and show the high stability of the LAr electronics over several months of data taking. First physics results concerning key calorimeter measurements like identification of photons, electrons, and missing tranverse energy are also shown.