Performance of the ATLAS LAr Calorimeter with Cosmic Muons and LHC Single Beam Data

The Liquid Argon (LAr) calorimeter is a key detector component in the ATLAS experiment at the LHC, designed to provide precision measurements of electrons, photons, jets and missing transverse energy. The LAr calorimeter has been installed in the ATLAS cavern and filled with liquid argon since 2006. Cosmic muon data, first triggered via specially developed trigger boards on the LVL1 output of the Tile calorimeter and later with the standard ATLAS LVL1 calorimeter trigger, have been recorded at various stages of commissioning. In Sept 2008, with the first single beams circulating in the LHC ring and a near full readout of the calorimeter, events resulting from beam-gas interactions and beam-collimator splash were recorded. We present here the calorimeter performance study based on these cosmic muon and LHC beam events. With the reconstructed muon minimum ionizing signal in the calorimeter, the uniformity of the barrel electromagnetic calorimeter can be checked. The timing alignment as measured from the data can be compared to the expectation. With the high energy depositions in the calorimeter readout cells, either from catastrophic energy loss of the cosmic muons or from beam interactions are used to validate the signal shape of calorimeter response derived from the calibration pulse.