Search for Neutrinoless Double Beta Decay with EXO-200

使用 EXO-200 搜索无中微子双贝塔衰变

• 批准号: 0653447
• 负责人: Carter Hall
• 金额: --
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-07-01 至 2010-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0653447&HistoricalAwards=false
• 关键词: Search; Neutrinoless; Double; Beta; Decay

Neutrinos are the most mysterious and elusive of the fundamental particles known to physics. Although their existence was conclusively established in the 1950's, only within the last decade has it been demonstrated that neutrinos have a non-zero mass. The discovery of neutrino mass raises some intriguing questions. For example, we know that the heaviest neutrino is at least a factor of 100,000 times lighter than the next heaviest particle, the electron. What can explain this wide disparity in mass scales? Is the origin of neutrino mass fundamentally different from the other particles? And is this related to the fact that neutrinos are the only constituents of matter that carry no electric charge?Neutrino physicists have concluded that these questions can best be addressed by studying a rare nuclear process known as neutrinoless double beta decay. Double beta decay is the conversion of two neutrons in an atomic nucleus into two protons, while emitting two electrons to conserve charge. This reaction, if it occurs in nature, would be mediated by the exchange of a neutrino. Consequently the half life of the decay is a measure of the absolute mass of the neutrino, a quantity which is still unknown. In addition, many grand unification theories, which attempt to unite three of the fundamental forces into one, either predict that double beta decay should occur, or predict that it should be forbidden. Therefore an experiment which can observe or rule out this process will play a key role in our understanding of matter at its most basic level.In this proposal, the PI requests funds to start a new group at the University of Maryland to collaborate on EXO-200, an experiment to search for the neutrinoless double beta decay of Xenon-136, and to significantly expand and broaden the tools used by the experiment to monitor, identify, and eliminate sources of electronegative impurities in the xenon. The experiment will begin taking data in 2007.In addition to the basic science goals described above, the research proposed here will have a significantly broader impact. The radiation detector technology being developed for EXO-200 has potential applications in other fields such as nuclear medicine and homeland security. The PI also proposes to initiate an outreach program in the public schools in Carlsbad New Mexico and the Shenandoah Valley of Virginia, both of which are underserved areas.

中微子是物理学已知的基本粒子中最神秘、最难以捉摸的。虽然中微子的存在早在1950年的S就已得到确凿的证实，但直到最近十年才被证明中微子具有非零质量。中微子质量的发现引发了一些有趣的问题。例如，我们知道最重的中微子至少比第二重的粒子电子轻10万倍。如何解释质量尺度上的巨大差异？中微子质量的起源与其他粒子有根本的不同吗？这是否与中微子是物质中唯一不带电荷的成分有关？中微子物理学家得出结论，这些问题最好可以通过研究一种罕见的核过程来解决，这种过程被称为无中微子双β衰变。双β衰变是原子核中的两个中子转化为两个质子，同时发射两个电子以保存电荷。这种反应，如果在自然界中发生的话，将通过中微子的交换来调节。因此，衰变的半衰期是对中微子绝对质量的测量，这个量仍然是未知的。此外，许多试图将三种基本力量统一为一种力量的大统一理论，要么预测应该发生双β衰变，要么预测应该禁止双β衰变。因此，一项能够观察或排除这一过程的实验将对我们在最基本的层面上理解物质起到关键作用。在这项提议中，PI请求资金在马里兰大学成立一个新的小组，在EXO-200上合作，这是一个寻找氙气-136的无中微子双β衰变的实验，并显著扩大和拓宽实验所使用的工具，以监测、识别和消除氙气中电负性杂质的来源。该实验将于2007年开始收集数据。除了上述基本科学目标外，这里提出的研究将产生更广泛的影响。正在为EXO-200开发的辐射探测器技术在其他领域有潜在的应用，如核医学和国土安全。PI还提议在新墨西哥州卡尔斯巴德和弗吉尼亚州谢南多阿山谷的公立学校启动一项外联计划，这两个地区都是服务不足的地区。