超低能量阈高纯锗探测器的暗物质直接探测

发布时间：2018-01-11 03:01

本文关键词：超低能量阈高纯锗探测器的暗物质直接探测　出处：《清华大学》2013年博士论文　论文类型：学位论文

【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。
[Abstract]:In 21th century, dark matter is one of the most basic subjects in physics. In recent years, the study of dark matter is very important for understanding the origin, evolution of the universe and the origin and interaction of matter. Direct detection of dark matter particles in low mass regions below 10 GeV 路c-2 has become a focus of dark matter research. This project is the first step of China Dark matter Experimental Project. A high purity germanium detector is used to search dark matter particles in a low mass region below 10 GeV 路c ~ (-2). In order to reduce the impact of environmental background on the case rate. The experiment was conducted at China JinPing underground LaboratoryCJPL, the world's deepest rock-covered underground laboratory in China. An excellent passive shielding system including polyethylene lead and oxygen free copper was constructed and an anti-Compton active shielding system was built using sodium iodide detector in order to obtain low energy threshold. Based on the 20g ultra-low energy threshold high purity germanium detector, the system includes detector and liquid nitrogen filling system, electronic signal processing and data acquisition system. After debugging and testing, the linear deviation of the experimental measuring device in the energy range below 9keV is less than 0.2. The energy resolution (half maximum width) is about 200eV at 5keV; The noise level (half-maximum width) reaches about 120eV, which can achieve the energy threshold of 220eV. these properties basically meet the requirements of dark matter experimental research in low mass region. In order to reduce the noise and chatter noise, a method based on signal time relationship and pulse shape is established in this paper. Through data quality check, physical case selection and efficiency correction. Finally, an effective energy spectrum of physical events is obtained. Based on the experimental data of 42 days, the theoretical model of elastic scattering and the statistical method of maximum gap method are used to make a detailed physical analysis. The results of the exclusion line for the two dimensional parameters of dark matter cross section and dark matter mass are given. The measurement sensitivity of dark matter particle mass in 2-4 GeV 路c-2 region is up to the best level in the world. On the other hand, in order to achieve higher sensitivity, CDEX is upgrading the germanium detector with higher quality. In this paper, the high purity germanium detector with 1kg P type point contact electrode has been tested and studied. Some new analytical methods of mass detectors are summarized, which provide a good reference for future dark matter research. The experiment of dark matter in low mass region has been carried out systematically by using 20g ultra-low energy threshold high purity germanium detector, which is the first attempt in China. It is based on the effective data of 0.207 kg 路day. In the low mass region of 2-4 GeV 路c ~ (-2) dark matter reaches the most sensitive level in the world. It also accumulates experience for the future study of dark matter in CDEX.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：P145.9

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