公斤级点电极高纯锗探测器的暗物质直接探测研究

发布时间：2018-02-26 19:21

本文关键词： 点电极高纯锗探测器低能量阈值低本底暗物质直接探测　出处：《清华大学》2016年博士论文　论文类型：学位论文

【摘要】：众多强有力的证据显示暗物质是宇宙的重要组成部分,但是迄今为止,其本质仍然未知。物理学家构建了许多模型来描述暗物质,其中弱作用大质量粒子是最流行的候选者之一。由于暗物质对物质起源和宇宙演化等具有十分重要的意义,因此暗物质已经成为当今基础物理研究的前沿和热点课题之一。直接探测法是研究暗物质最直接和有效的方法之一。有多个实验已经在10 GeV/c2质量附近发现了疑似暗物质事例,因此这个质量区域已经成为暗物质研究的焦点。本课题利用世界上第一个公斤级的点电极高纯锗探测器设计和研制了暗物质直接探测研究实验系统,旨在对10 GeV/c2的质量区间进行探测,给出暗物质在“质量-反应截面”参数空间中的灵敏度曲线。为了降低点电极高纯锗探测器的本底水平,实验在世界最深的中国锦屏地下实验室开展,搭建了有效的被动屏蔽体系统,并且利用低本底的NaI(Tl)反符合探测器作为主动屏蔽体进一步降低本底。针对实验系统的不同噪声来源,发展了基于时间和波形信息的信号甄别方法。特别地,针对本课题中脉冲反馈电荷灵敏前放的一种特定电子学噪声,发展了一种时间关联性甄别技术,将实验系统的能量阈值从1 keVee(1)降低到了400 eVee,达到了国际同类型探测器的最低阈值;同时,发展了反康普顿事例甄别技术和针对P型点电极高纯锗探测器的体/表面事例甄别技术,极大地降低了本底水平,其中在3-6 keVee能量区间的本底水平达到了约4 cpkkd(2)。这两个特性使得此实验系统对低质量(10 GeV/c2)暗物质的探测灵敏度具有很强的国际竞争力。本课题利用365天的有效本底数据,经过数据处理得到物理能谱,再扣除掉点电极高纯锗探测器自身的宇生放射性核素和高能γ射线在低能区的贡献,最后得到可能由暗物质贡献的能谱。通过暗物质与靶核的弹性散射作用模型和最小二乘法的统计分析方法,得到了暗物质的灵敏度曲线。对于自旋无关反应,在低质量区域的实验结果达到了国际一流的水平,排除了10 GeV/c2质量附近的大部分疑似暗物质区域,特别是完全排除了采用类似探测技术的CoGeNT实验组给出的信号区域。对于自旋相关反应,完全排除了DAMA实验组给出的10 GeV/c2质量附近的信号区域,并且在4-7 GeV/c2的质量区域,达到了国际最灵敏的水平。
[Abstract]:There is strong evidence that dark matter is an important part of the universe, but so far its nature is still unknown. Physicists have built many models to describe dark matter. One of the most popular candidates is the weak-acting mass particle. Since dark matter is of great significance to the origin of matter and the evolution of the universe, Direct detection is one of the most direct and effective methods to study dark matter. Several experiments have found suspected dark matter cases near 10 GeV/c2 mass. Therefore, this mass region has become the focus of dark matter research. In this paper, we have designed and developed an experimental system for direct detection of dark matter using the first spot electrode high purity germanium detector of the world's first kilogram class. In order to detect the mass range of 10 GeV/c2, and give the sensitivity curve of dark matter in the "mass-reaction cross section" parameter space, in order to reduce the background level of the point electrode high purity germanium detector, The experiment was carried out in the world's deepest underground laboratory in Jinping, China, and an effective passive shield system was built. And using the low background NAI Tl) anti-coincidence detector as the active shield to further reduce the background. According to the different noise sources of the experimental system, a signal discrimination method based on time and waveform information is developed. In particular, For a particular electronic noise of pulse feedback charge sensitive forward amplifier in this paper, a time-dependent discrimination technique is developed. The energy threshold of the experimental system was reduced from 1 keVee1) to 400 eVees, which reached the minimum threshold of the same type of detectors in the world. At the same time, The development of the anti-Compton case screening technique and the bulk / surface case screening technique for the P-type point electrode high purity germanium detector have greatly reduced the background level. The background level in the 3-6 keVee energy range is about 4 cpkkd2. These two characteristics make this experimental system highly competitive in detecting dark matter with low mass of 10 GeV / c2.In this paper, we use the effective background data of 365 days. After data processing, the physical energy spectrum is obtained, and the contribution of the eugenic radionuclides and high energy 纬 rays of the high purity germanium detector of the point electrode in the low energy region is deducted. Finally, the energy spectrum, which may be contributed by dark matter, is obtained. The sensitivity curve of dark matter is obtained by using the elastic scattering model of dark matter and target nucleus and the statistical analysis method of least square method. The experimental results in low-mass areas reached a world-class level, excluding most suspected dark matter areas near the mass of 10 GeV/c2. In particular, the signal region given by the CoGeNT experimental group using similar detection techniques is completely excluded. For the spin correlation reaction, the signal region near the 10 GeV/c2 mass given by the DAMA experimental group is completely excluded, and the mass region of 4-7 GeV/c2 is excluded. Reached the most sensitive level in the world.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P145.9

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