Study of ATLAS Tile Calorimeter response uniformity using muon beams

ATLAS is a general purpose experiment designed to explore the physics landscape in proton- proton collisions at the unprecedentedly high energy regime of the Large Hadron Collider at CERN. The Tile Calorimeter (TileCal) is a sampling plastic scintillator/iron detector and provides accurate energy and position measurements of electrons, photons, isolated hadrons, jets, and transverse missing energy, as well as helping in particle identification and in muon momentum reconstruction. TileCal is divided into three cylindrical sections referred to as the long barrel (LB) and two extended barrels (EB). Each of the three TileCal barrels is composed of 64 azimuthal segments, referred to as modules. Each barrel consists of several layers. The Large Hadron Collider (LHC) Phase ll upgrade aims to increase the accelerator luminosity by a factor of 5-10. Due to the expected higher radiation levels and the aging of the current electronics, a new readout system of the ATLAS experiment hadronic calorimeter (TileCal) is needed that will be able to process increased data input. A hybrid prototype of the upgrade TileCal – Demontrator has been tested using the beam of different particles from the Super Proton Synchrotron (SPS) accelerator at CERN. Data were collected with the beams of muons, electrons and hadrons at various incident energies and impact angles. The high energy muons traverse the entire TileCal modules for any angle of incidence, thereby allowing a study of the module response in great detail through their entire volume. Muon beam (165 GeV energy, -90° angle) was used to test the module and afterwards collected data was analyzed. The dominant energy loss process is ionization and the energy loss is essentially proportional to the muon track path length. The dE/dx (energy loss per unit of length) distributions were obtained and analyzed for each cell of A, BC and D layers, with expectations that dE/dx value in each cell will be nearly equal, i.e. distribution of dE/dx will be flat. As a result of the analysis the new electronics good performance was verified, expected muon behavior was obtained, i.e. muon energy loss per unit of length was approximately similar in each cell of the studied layers that proves the homogeneity of the tested module.