DUSEL R&D towards a tonne scale Ge neutrinoless double-beta decay experiment

随着人们认识到中微子的质量很大，人们对研究中微子的本征性质越来越感兴趣。了解中微子的质量产生机制、绝对中微子质量标度和中微子质量谱是未来中微子实验的重点之一。无中微子双β衰变(NDBD)的实验证据将确定中微子的Majorana性质，同时也提供关于绝对中微子质量的信息。该合同将使Majorana合作能够开展与开发拟议的Majorana示范器相关的研发活动，这是一个旨在证明未来1吨Ge NDBD实验的可行性的Ge探测器阵列原型。这项研究将在两个不同的领域进行：Ge探测器的开发和超低本底材料的生产和分析。要建立一个能够探测倒置层级区域中微子质量的NDBD实验，需要将对NDBD敏感的大质量探测器(大约1吨)和前所未有的本底水平(NDBD信号区每年大约或不到1次计数)结合在一起。他们计划部署和评估两种不同的Ge探测器技术，一种基于P型材料，另一种基于N型材料。Dusel正在考虑的最初一系列实验中的许多将直接受益于超清洁材料的可用性，其中含有极少量的U和Th。要验证材料的纯度，需要达到亚微Bq/kg级别的灵敏度。高灵敏度电感耦合等离子体质谱的发展将有利于更广泛的应用和未来的实验。GE探测器的开发将有利于需要非常低的能量阈值的应用，同时还提供相关探测器组件的减少的背景。

With the realization that neutrinos are massive, there is an increased interest in investigating their intrinsic properties. Understanding the neutrino mass generation mechanism, the absolute neutrino mass scale and the neutrino mass spectrum are some of the main focuses of future neutrino experiments. Experimental evidence of neutrinoless double-beta decay (NDBD) would definitively establish the Majorana nature of neutrinos while also providing information about the absolute neutrino mass. This award will enable the Majorana Collaboration to carry out R&D activities related to the development of the proposed Majorana Demonstrator, a prototype Ge detector array that aims to prove the feasibility of building a future 1-tonne Ge NDBD experiment. The research would be conducted by the collaboration in two distinct areas: Ge detector development and the production and assay of ultra-low background materials. Building a NDBD experiment with the ability to probe neutrino mass in the inverted hierarchy region requires the combination of a large detector mass sensitive to NDBD, on the order of 1-tonne, and unprecedented background levels, on the order of or less than 1 count per year in the NDBD signal region. They plan to deploy and evaluate two different Ge detector technologies, one based on P-type material and the other on N-type. Many of the initial suite of experiments being considered for DUSEL will directly benefit from the availability of ultra-clean materials with extremely small amounts of U and Th. Verifying the purity of materials requires sensitivities at the sub microBq/kg level. The development of enhanced sensitivity inductively coupled plasma mass spectrometry will benefit a broad set of applications and future experiments. The Ge detector development will benefit applications that require very low energy thresholds while also providing reduced backgrounds from associated detector components.