Performance of the ATLAS Liquid Argon Calorimeter with cosmic muons and single LHC beam data

The Liquid Argon (LAr) calorimeter is a key detector in the ATLAS (A Toroidal LHC ApparatuS) experiment at the Large Hadron Collider (LHC), designed to provide precision measurements of electrons, photons, jets and missing transverse energy. Cosmic muon data has been recorded by the LAr calorimeter at various stages of commissioning, with the first single LHC beam data being recorded in September 2008. We present here the LAr calorimeter performance studies based on cosmic muons and LHC beam data. In 2008, ~99% of the LAr readout channels were fully operational. The high energy deposits in the calorimeter readout cells have been used to validate the signal shape reconstruction from calibration predictions at a level better than ~2% The measured timing alignment agrees with expectations at the 2 ns level. The non-uniformity of the barrel electromagnetic (EM) calorimeter has been estimated less than 2% thanks to cosmic muons.