Dark Matter Direct Detection Research With 1kg-scale P-type Point-contact High Purity Germanium Detector

A great many of compelling evidences have revealed that dark matter is one important component of the Universe,however,its nature remains unknown so far.The physicists have constructed enormous models to describe dark matter,and the weakly interacting massive particle(WIMP)is one kind of the most popular candidates.Since dark matter is significant to understand the origin of mass and the evolution of the Universe,it has become one of the frontier and hot topics in the fundamental physics research.The direct detection of dark matter is thought to be the one of the most promising and significant methods.Until now,some direct detection experiments have announced that some signal regions of dark matter have already been found around 10GeV/c2.Therefore,it makes this mass region to be the most attractive one.This dissertation work aims at direct detection of dark matter with point-contact high purity germanium detector(PCGe)which is the first one at1kg-scale mass in the world,focusing on verifying the dark matter signal regions around 10 Ge V/c2 and giving the exclusion limits on the parameter space of the mass and cross section of dark matter.To suppress the contributions from background,the experiment located in China Jin Ping underground laboratory(CJPL)which is the deepest in the world,and one effective passive shielding system was constructed.In addition,the Na I(Tl)anti-compton detector was applied as active shielding system to further decrease the background level.Different methods based on timing information and pulse shape characteristics were developed to discriminate various sources of noise in the experiment.In especially,an innovative method originating from the timing correlations of events was derived to eliminate one kind of the specific electronic noise induced by the pulsed reset feedback preamplifier,which reduced the energy threshold of the PCGe from 1 ke Vee down to 400 e Vee.Besides,the anti-compton events and bulk/surface events for p-type PCGe discrimination methods were developed to suppress the background level,leading to about 4 cpkkd at 3-6 ke Vee.These advantages make the system to bestrong international competitive on sensitivity for low mass(<10 Ge V/c2)dark matter search.Based on the 365 day's valid background data,the possible recoil spectrum of dark matter was achieved through the data analysis and known background subtraction including the budget from the cosmogenic nuclides of the PCGe itself and the contribution induced by high energy gamma rays.The exclusion plots in the parameter space of dark matter mass and cross section were carried out by combining the elastic scattering model and minimal chi-square statistical method.For spin-independent cross section,the sensitivities get to the first class level in the world,excluding most of the signal region around 10 Ge V/c2,especially the whole signal region proposed by Co Ge NT whose detection technology is similar.As to sin-dependent cross section,the results totally exclude the DAMA allowed region around 10 Ge V/c2,and give the most stringent limits at the mass region of 4-7 Ge V/c2.