Liquid argon scintillation response to electronic recoils between 2.8–1275 keV in a high light yield single-phase detector

We measure the liquid argon scintillation response to electronic recoils in the energy range of 2.82 to 1274.6 keV at null electric field. The single-phase detector with a large optical coverage used in this measurement yields 12.8 ± 0.3 ( 11.2 ± 0.3 ) photoelectron / keV for 511.0-keV γ -ray events based on a photomultiplier tube single photoelectron response modeling with a Gaussian plus an additional exponential term (with only a Gaussian term). It is exposed to a variety of calibration sources such as 22Na and 241Am γ-ray emitters, and a 252Cf fast neutron emitter that induces quasimonoenergetic γ rays through a ( n, n′γ ) reaction with 19F in polytetrafluoroethylene. In addition, the high light detection efficiency of the detector enables identification of the 2.82-keV peak of 37Ar, a cosmogenic isotope in atmospheric argon. The observed light yield and energy resolution of the detector are obtained by the full-absorption peaks. We find up to approximately 25% shift in the scintillation yield across the energy range and 3% of the energy resolution for the 511.0-keV line. The Thomas-Imel box model with its constant parameter ... is found to explain the result. For liquid argon, this is the first measurement on the energy-dependent scintillation yield down to a few keV at null field and provides essential inputs for tuning the argon response model to be used for physics experiments. (ProQuest: ... denotes formula omitted.).