Readiness of the ATLAS liquid argon calorimeter for LHC collisions

Abstract

The ATLAS liquid argon calorimeter has been operating continuously since August 2006. At this time, only part of the calorimeter was readout, but since the beginning of 2008, all calorimeter cells have been connected to the ATLAS readout system in preparation for LHC collisions. This paper gives an overview of the liquid argon calorimeter performance measured in situ with random triggers, calibration data, cosmic muons, and LHC beam splash events. Results on the detector operation, timing perfore-mail: atlas.secretariat@cern.ch mance, electronics noise, and gain stability are presented. High energy deposits from radiative cosmic muons and beam splash events allow to check the intrinsic constant term of the energy resolution. The uniformity of the electromagnetic barrel calorimeter response along η (averaged over φ) is measured at the percent level using minimum ionizing cosmic muons. Finally, studies of electromagnetic showers from radiative muons have been used to cross-check the Monte Carlo simulation. The performance results obtained using the ATLAS readout, data acquisition, and reconstruction software indicate that the liquid argon calorimeter is well-prepared for collisions at the dawn of the LHC era.

Studies of the performance of the ATLAS detector using cosmic-ray muons

“…J. C ( ) 71: 1593 events have been previously exploited for pulse shape studies of the LAr calorimeter and as a source of photons used to validate the photon-identification capabilities of the ATLAS EM calorimeter [7,11].…”

“…These can be particularly important in the case of high-energy muons, which can lose a significant amount of energy between the two tracking detectors. Such events have been previously exploited for pulse shape studies of the LAr calorimeter and as a source of photons used to validate the photon-identification capabilities of the ATLAS EM calorimeter [7,11].…”

“…So, in addition to subdetector-specific cosmic-ray studies, these cosmic-ray data samples provide the first opportunity to study the combined performance of different detector components. Subsystem-specific cosmic-ray commissioning results have been documented in a series of separate publications [6][7][8][9]. This paper presents the results of studies relevant to combined tracking performance, lepton identification and calorimeter performance for the reconstruction of jets and missing transverse energy.…”

“…J. C ( ) 71: 1593 events have been previously exploited for pulse shape studies of the LAr calorimeter and as a source of photons used to validate the photon-identification capabilities of the ATLAS EM calorimeter [7,11].The reconstruction of cosmic-ray events is also complicated by the fact that they occur at random times with respect to the 40 MHz readout clock, which is synchronized to the LHC clock during normal operation. For each subsystem, reconstruction of these events therefore first requires some measure of the event time with respect to the readout clock.…”

“…These differences can be addressed in the event reconstruction and data analysis. The modifications required for reconstruction of these events in the different detector components are discussed in the subsystemspecific cosmic-ray commissioning papers [6][7][8][9]. …”