ATLAS Liquid Argon Calorimeter Pulse Shape Reconstruction And Analysis

Abstract

The ATLAS detector of the Large Hadron Collider (LHC) records data from proton-proton collisions at the highest energy available in laboratory. It uses a Liquid Argon (LAr) calorimeter system to measure the energy of particles created in these proton-proton collisions. In normal data taking runs, only 4 digital samples of the LAr calorimeter readout signals is recorded, and a measure of energy is derived from these 4 digital samples. The precision at which the amount of energy deposited in a calorimeter cell can be measured depends directly on the knowledge of the exact calorimether pulse shape. In April 2018, special data taking runs were taken that allowed a total of 32 digital samples to be recorded, allowing a full in-situ reconstruction of the signal pulses from every individual readout cells in the calorimeter system. A unique time granularity of 3.125 ns of the signal is obtained by taking into account data collected with different readout time shifts. The reconstructed pulse shapes are used for data driven comparison with calibration and simulation signals to further improve the latter. Example of pulse shape comparison will be presented. A preliminary analysis of the ionization charge drift time in the calorimeter barrel region will also be discussed. Detector sagging under gravity affects the width of the LAr gaps which in turn affects the ionization charge drift time. The effect is quantified by analysing the calorimeter pulse duration as a function of azimuthal angle in the detector.