Energy linearity and resolution of the ATLAS electromagnetic barrel calorimeter in an electron test-beam

Abstract

ATLAS Electromagnetic Barrel Calorimeter CollaborationA module of the ATLAS electromagnetic barrel liquid argon calorimeter was exposed to the CERN electron test-beam at the H8 beam line upgraded for precision momentum measurement. The available energies of the electron beam ranged from 10 to 245 GeV. The electron beam impinged at one point corresponding to a pseudo-rapidity of eta=0.687 and an azimuthal angle of phi=0.28 in the ATLAS coordinate system. A detailed study of several effects biasing the electron energy measurement allowed an energy reconstruction procedure to be developed that ensures a good linearity and a good resolution. Use is made of detailed Monte Carlo simulations based on Geant which describe the longitudinal and transverse shower profiles as well as the energy distributions. For electron energies between 15 GeV and 180 GeV the deviation of the measured incident electron energy over the beam energy is within 0.1%. The systematic uncertainty of the measurement is about 0.1% at low energies and negligible at high energies. The energy resolution is found to be about 10% sqrt(E) for the sampling term and about 0.2% for the local constant term

Measurement of the Inclusive Jet Cross Section with the ATLAS Detector at the Large Hadron Collider

“…If the event is retained by the trigger signal (see Section 2.9), a number of samples (5 or 7) are digitised and sent to the off-detector electronics for calibration. The full electronic calibration procedure to convert the raw signal to a pulse shape in ADC counts such as the one in Figure 2.8 and to extract the visible energy deposited in each cell is described in detail in References [64][65][66].…”

“…The cluster energy and position needs to be determined precisely starting from the visible energy deposited in the cells and taking into account the shower development in the sampling calorimeters, the energy deposited upstream the calorimeter (using information from the presampler), the leakage outside the calorimeters and the modulations of the energy in η and φ due to the accordion geometry. These factors and the calibration constants for the electronics (including corrections for known high voltage problems) have been derived and validated using electron and muon test beams and Monte Carlo simulation [65,[70][71][72][73][74][75][76]. The systematic uncertainty on the electron energy scale after this calibration procedure amounts to 3%.…”

“…• The difference in the electromagnetic scale between the test-beam setup and the full ATLAS detector due to the uncertainty in the liquid argon temperature in the test-beam, derived from comparison of different test-beam measurements [65,72];…”

“…An optimal filtering algorithm is used to extract the amplitude, timing and pedestal from the pulse shape [79]. The ADC counts that are the output of the photomultipliers are converted into an energy measurement using correction constants derived from test beam measurements [65,[71][72][73]80] and propagated to the full ATLAS setup using a charge injection calibration system [79]. The absolute calorimeter response to energy deposited via electromagnetic processes has also been validated in the hadronic calorimeters using muons, both from test-beams [80] and produced by cosmic-rays in-situ [81].…”

Combined performance studies for electrons at the 2004 ATLAS combined test-beam

“…The used LAr calorimeter module will be described in more detail in section 2. Its performance has been measured in many test-beam campaigns, the results on linearity, uniformity and resolution for the LAr barrel calorimeter have been published in [12] and [13] for "close-to-ideal" conditions, with very little material upstream the calorimeter, with no other ATLAS detectors being operated simultaneously (potential sources of coherent noise) and without any magnetic field. The electron performance of the LAr barrel calorimeter at the CTB, including linearity, uniformity, and resolution with different amounts of material upstream the calorimeter and momenta ranging from 1 GeV to 250 GeV/c without magnetic field in the Inner Detector has been published in [14].…”