Response of D -Zero uranium liquid argon calorimeters at low energies and the effect of oxygen contamination on observed signals

Fermi National Accelerator Lab (Fermilab) is the site of the world's highest energy particle accelerator. The D-Zero experiment is one of two at Fermilab studying proton-antiproton collisions at center of mass energies of 1.8 TeV. An analysis of the response of the D-Zero central calorimeter to single electrons and pions has been performed under a variety of operating conditions. The data were acquired from the Load-2 D-Zero Test Beam run, in which beam tests of calorimeter modules were performed between July 1991 and January 1992.;The response of modules from the D-Zero central calorimeter was obtained for single electrons and pions in the energy range of 2 through 150 GeV, and implications of these measurements were explored for the energy response to hadronic jets in the calorimeter.;The effects of added oxygen, tetramethylgermanium (TMG), and nitrogen for the responses of the calorimeter modules were examined. The additives were found to have similar effects on the signals from electrons and pions. The data with added oxygen were used to calibrate the response of the calorimeter to oxygen concentration in the liquid argon, as measured using the D-Zero liquid argon purity monitoring system.;The response of the calorimeter to electrons and pions was also studied for varying charge collection fields. An analysis of the data suggests that the signal (ionization) in typical pion showers contains a greater amount of dense ionization than for the case of electron showers. However, the difference was not found to be sufficiently large enough to allow improvement of compensation in the calorimeter by the addition of photosensitive dopants or by operating at higher charge collection fields.