Measurement of pion and proton response and longitudinal shower profiles up to 20 nuclear interaction lengths with the ATLAS Tile calorimeter

The response of pionsand protons in the energy range of 20–180 GeV, produced at CERN's SPS H8 test-beam line in the ATLAS iron–scintillator Tile hadron calorimeter, has been measured. The test-beam configuration allowed the measurement of the longitudinal showerdevelopment for pionsand protons up to 20 nuclear interaction lengths. It was found that pionspenetrate deeper in the calorimeterthan protons. However, protons induce showersthat are wider laterally to the direction of the impinging particle. Including the measured total energy response, the pion-to-proton energy ratio and the resolution, all observations are consistent with a higher electromagnetic energy fraction in pion-induced showers. The data are compared with GEANT4 simulations using several hadronic physics lists. The measured longitudinal showerprofiles are described by an analytical showerparametrization within an accuracy of 5–10%. The amount of energy leaking out behind the calorimeteris determined and parametrized as a function of the beam energy and the calorimeterdepth. This allows for a leakage correction of test-beam results in the standard projective geometry.