Key Technology Research of Liquid Argon Veto Detector in CDEX

​The China Dark Matter Experiment (CDEX) Collaboration has been aiming to search for low mass WIMPs with a ton-scale highly pure germanium (HPGe) detector. In order to suppress the background, an anti-coincidence veto detector is employed in CDEX, acting as the active shielding. However, active shielding system with solid scintillators has to be abandoned as the Ge detector get larger in the following phases of CDEX experiments. The Liquid Argon (LAr) veto is proposed in the second phase CDEX-10 which is the first dark matter direct detection experiment using LAr detector as an anti-coincidence veto detector. My research work is focused on the R&D of CDEX-10 LAr veto detector, which contains:
(1) Designing and building a prototype of the liquid argon detector. The principle of the LAr detector experiment and the operating processes have been mastered. The methods of data analysis have been developed. All of these will help to the operation of the CDEX-10 LAr veto detector.
(2) Measurement and the Monte Carlo simulation of the photoelectron yield of the prototype LAr detector. The photoelectron yields of the prototype LAr detector have been measured to be 0.051-0.079 p.e./keV for 662 keV γ lines at different positions. The Monte Carlo simulation provided a better understanding of the spectra we obtained.
(3) Research of pulse shape of the LAr scintillation lights. The pulse shape discrimination of γ particles and α particles has been studied. The prompt fraction Fprompt was found to be different between the γ particles and α particles, which provides the possibility to develop the pulse shape discrimination method of the LAr detector which is unpurified. In addition, the relationship between the slow component lifetime of Ar scintillation lights and the Ar purity has also been studied. The purity of LAr can be monitored through this method.
(4) The performance of the CDEX-10 LAr veto detector has been estimated by Monte Carlo simulation. The energy threshold and the veto efficiency of the LAr veto detector was got through simulation. The background of CDEX-10 was simulated to be < 0.1 cpkkd after the active shielding of the LAr veto detector.