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  本文關鍵詞： 點電極高純鍺探測器 低能量閾值 低本底 暗物質 直接探測　出處：《清華大學》2016年博士論文　論文類型：學位論文

【摘要】：眾多強有力的證據(jù)顯示暗物質是宇宙的重要組成部分,但是迄今為止,其本質仍然未知。物理學家構建了許多模型來描述暗物質,其中弱作用大質量粒子是最流行的候選者之一。由于暗物質對物質起源和宇宙演化等具有十分重要的意義,因此暗物質已經(jīng)成為當今基礎物理研究的前沿和熱點課題之一。直接探測法是研究暗物質最直接和有效的方法之一。有多個實驗已經(jīng)在10 GeV/c2質量附近發(fā)現(xiàn)了疑似暗物質事例,因此這個質量區(qū)域已經(jīng)成為暗物質研究的焦點。本課題利用世界上第一個公斤級的點電極高純鍺探測器設計和研制了暗物質直接探測研究實驗系統(tǒng),旨在對10 GeV/c2的質量區(qū)間進行探測,給出暗物質在“質量-反應截面”參數(shù)空間中的靈敏度曲線。為了降低點電極高純鍺探測器的本底水平,實驗在世界最深的中國錦屏地下實驗室開展,搭建了有效的被動屏蔽體系統(tǒng),并且利用低本底的NaI(Tl)反符合探測器作為主動屏蔽體進一步降低本底。針對實驗系統(tǒng)的不同噪聲來源,發(fā)展了基于時間和波形信息的信號甄別方法。特別地,針對本課題中脈沖反饋電荷靈敏前放的一種特定電子學噪聲,發(fā)展了一種時間關聯(lián)性甄別技術,將實驗系統(tǒng)的能量閾值從1 keVee(1)降低到了400 eVee,達到了國際同類型探測器的最低閾值;同時,發(fā)展了反康普頓事例甄別技術和針對P型點電極高純鍺探測器的體/表面事例甄別技術,極大地降低了本底水平,其中在3-6 keVee能量區(qū)間的本底水平達到了約4 cpkkd(2)。這兩個特性使得此實驗系統(tǒng)對低質量(10 GeV/c2)暗物質的探測靈敏度具有很強的國際競爭力。本課題利用365天的有效本底數(shù)據(jù),經(jīng)過數(shù)據(jù)處理得到物理能譜,再扣除掉點電極高純鍺探測器自身的宇生放射性核素和高能γ射線在低能區(qū)的貢獻,最后得到可能由暗物質貢獻的能譜。通過暗物質與靶核的彈性散射作用模型和最小二乘法的統(tǒng)計分析方法,得到了暗物質的靈敏度曲線。對于自旋無關反應,在低質量區(qū)域的實驗結果達到了國際一流的水平,排除了10 GeV/c2質量附近的大部分疑似暗物質區(qū)域,特別是完全排除了采用類似探測技術的CoGeNT實驗組給出的信號區(qū)域。對于自旋相關反應,完全排除了DAMA實驗組給出的10 GeV/c2質量附近的信號區(qū)域,并且在4-7 GeV/c2的質量區(qū)域,達到了國際最靈敏的水平。
[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 緯 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.
【學位授予單位】：清華大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：P145.9

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本文編號：1539338