Calibration of a liquid xenon gamma ray detector for the study of radiative pion decay

The performance of a liquid xenon time projection chamber as a detector for gamma rays between 0 and 30 MeV has been studied by comparing data collected with radioactive sources to a Monte Carlo simulation. The detector was designed for the study of the pion radiative decay. Both the scintillation light and the ionization charge signals were exploited. The light signals were used in the trigger logic and for the measurement of the chamber trigger acceptance. The minimum triggerable energy turned out to be 170 keV. The charge signals were used to measure the gamma ray energy. The noise introduced by the electronics was about 140 keV and the minimum measurable energy 230 keV with an electric drift field of 0.5 kV/cm. All the charge and light spectra were in good agreement with the simulation. The overall apparatus acceptance, taking into account geometry, trigger efficiency and offline reconstruction losses, was independent of the gamma ray energy above 2 MeV and equal to 10%.