【作者】 吴昱城；

【导师】 李元景；

【作者基本信息】 清华大学 ， 核科学与技术， 2013， 博士

【摘要】 暗物质是21世纪物理学最基本的课题之一。暗物质研究对于认识宇宙的起源、演变以及物质的本源、相互作用都有着十分重要的意义。近年来，10GeV·c-2以下低质量区域的暗物质粒子直接探测成为了暗物质研究的一个焦点。本课题作为中国暗物质实验（ChinaDark matter EXperiment，CDEX）研究项目的第一步，使用高纯锗探测器在10GeV·c-2以下的低质量区进行暗物质粒子的搜寻。为了降低环境本底对事例率的影响，实验选在了世界上岩石覆盖最深的中国锦屏地下实验室（China JinPing underground Laboratory，CJPL），构建了包括聚乙烯、铅、无氧铜等在内的优良的被动屏蔽系统，并且采用碘化钠探测器搭建了反康普顿主动屏蔽系统。为了获得低的能量阈值，本课题以20g超低能量阈高纯锗探测器为主体建立了包括探测器及液氮灌装系统，电子学信号处理及数据获取系统，数据采集软件系统三大部分的实验测量装置。经过调试与测试，该实验测量装置在9keV以下能区的线性偏离小于0.2%；在5keV的能量分辨率（半高宽）达到约200eV；噪声水平（半高宽）达到约120eV，可以实现220eV的能量阈值。这些性能基本满足低质量区暗物质实验研究的要求。为了降低噪声和颤噪等干扰，本课题建立了基于信号时间关系以及脉冲形状的分析方法，通过数据质量检查、物理事例筛选及效率修正，最终得出有效的物理事例能谱。本课题基于42天的实验数据，采用弹性散射理论模型和最大间隙法的统计学方法做了仔细的物理分析，给出了暗物质截面和暗物质质量二维参数的排除线结果。暗物质粒子质量在2-4GeV·c-2区域的测量灵敏度达到了国际最好的水平。另一方面，为了实现更高的灵敏度，CDEX正在升级更大质量的锗探测器。本课题对1kg P型点接触电极高纯锗探测器进行了测试研究，总结了大质量探测器的一些新的分析方法，为今后开展暗物质研究提供了良好借鉴。本课题利用20g超低能量阈高纯锗探测器系统地开展了低质量区的暗物质实验研究，是国内的首次尝试。基于0.207kg·day的有效数据，在2-4GeV·c-2的暗物质低质量区达到了国际最灵敏的水平。同时为CDEX今后的暗物质实验研究积累了经验。更多还原

【Abstract】 Dark matter is one of the most fundamental subjects of physics in the21st century.Research of dark matter holds great significance to the extent that it can helpunderstanding the origin and evolution of our universe, as well as the basis andinteraction of matter. The direct detection of dark matter searches in the low massregion under10GeV·c-2becomes a new research topic of focus in recent years.As the first step of China Dark matter EXperiment (CDEX) project, thisdissertation work is focused on dark matter searching in the low mass region (below10GeV·c-2) with High-purity Germanium detector.To lower the background event rate, we set up our experiment in the world’sdeepest rock overburden China JinPing underground Laboratory, constructed a superiorpassive shielding system containing polyethylene, lead, copper, etc., and applied ananti-Compton active shielding system with a NaI detector. To practice low energythreshold, a20g Ultra-Low Energy threshold Germanium detector (20g-ULEGe) wasused as the essential part of the experiment setup, which included the detector and liquidnitrogen filling system, the electronics system of signal processing and data taking, andthe DAQ software system. Through the commissioning and testing, the experimentsetup realized an energy nonlinearity of less than0.2%below9keV, an energyresolution (full width at half maximum) of around200eV, and a noise level of roughly120eV which can provide potential merit of220eV energy threshold. These goodperformances are able to meet the demand of dark matter research below10GeV·c-2low mass region.A data analysis method based on time relationship and pulse shape characteristicswas established to filter noise and microphonics events. Data quality check, physicsevent selection and corresponding efficiency correction are carried out to derive thespectrum of selected physics events.With the experiment data of42days’ livetime, physics interpretation was carefullycarried out using elastic scattering theory and the maximum gap statistical method. Theexclusion curve in the parameter space of cross section and dark matter mass was plotted.The result shows the most sensitive behavior of dark matter searches at2-4GeV·c-2in the world.On the other hand, CDEX is upgrading more massive germanium detectors toachieve better sensitivity. A1kg P-type Point Contact Germanium detector was set upand tested. Several new analysis methods were summarized for the larger detector,which could be a good reference for its upcoming dark matter research.The attempt of dark matter detection using20g-ULEGe in the low mass regionincluded in this dissertation is the first dark matter direct detection in China. The mostsensitive result within2-4GeV·c-2was achieved with0.207kg·day’s effective data.This work underlies further dark matter research of the CDEX new phase project.更多还原