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.