Searching For Low Mass Dark Matter With The PandaX Liquid Xenon Detector

Numbers of astronomical observations, associated with large-scale simulations, show the evidence of the existence of dark matter. Over the last 30 years, direct searching of dark matter candidate particles, the weakly interacting massive particles(WIMPs), have attracted great attention.Among various techniques used in the dark matter searching experiments,dual-phase time projection chamber using liquid xenon as target material(LXe-TPC) is the most promising one so far. It has the advantages of strong rejection level for gamma background rays and high 3-D position sensitivity.The great rejection power against the gamma background of LXeTPC comes from the distinct charge-to-photon ratio between the electron recoil and nuclear recoil events induced by gamma rays and WIMPs(as well as neutrons), respectively, in liquid xenon. However, there’re still several properties missing in our understanding of the signals in liquid xenon, one of which is the limitation of the rejection power in low energy.In the present thesis, the construction of a mini LXe-TPC is introduced in Chapter 3, including the crogenic, recirculation, data taking and offline analysis systems. Using such a detector, we reached very high energy resolution, allowing to investigate the property of the low energy region in LXe for both electron and nuclear recoils with a minimum detector-induced fluctuation. Such properties were very poorly measured previously, and out results bring new prospect of LXe-TPC and help in optimizing it. The measurements of the low energy events in such a detector and the model of the recombination fluctuation in low energy region in LXe are illustrated in Chapter 4.Chapter 5 will be devoted to illustrate the PandaX Rawdata Processor(PRP), one of the data processing and offline analysis systems of a large underground experiment for dark matter direct searching – PandaX.PandaX is the first dark matter searching experiment using time projection chamber as its detection technique in China. It is located in China Jinping underground Lab(CJPL) in Sichuan. The lab has a world-record depth of about 6900 meter water equivalence, and provides an extremely low muon-induced background. PandaX has published its first paper in Augest this year, excluding all the previously reported positive results for low mass dark matter around 10 GeV. The analyses of the low mass dark matter signals in PandaX first scientific data are illustrated in Chapter 5 as well.