Analysis of signal waveform from a midsize liquid argon detetor

The tonnage liquid argon prototype detector is a midsize single phase liquid argon detector running in the ground lab. Scintillation light from the liquid argon (LAr) is collected by 42 8-inch photomultiplier tubes (PMT). Analyzing the signal waveform can give key characteristics of the detector, such as the slow decay time constant labeling the purity of the liquid argon. Based on the classical liquid argon light emission theory including fast and slow components of light decay process, a model considering the TPB re-emission process and the signal reflection effects is proposed. TPB re-emission process is introduced with three exponential time structure. Furthermore, the post-peak hump structure is validated to be signal reflections.The model predicts signal waveforms of events from both the electron recoil and nuclear recoil.