Search for neutrino-less double beta decay with EXO-200 and nEXO

使用 EXO-200 和 nEXO 寻找无中微子双 β 衰变

• 批准号: SAPPJ-2016-00037
• 负责人: Brunner, Thomas
• 金额: $ 2.99万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Subatomic Physics Envelope - Project
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=616852
• 关键词: Search; neutrino; less; double; beta

The search for lepton-number violating zero neutrino double-beta decays (bb0n) is one of the main challenges in today’s particle physics. Observation of this decay would require the neutrino to be a Majorana particle. The EXO-200 collaboration is currently searching for bb0n decay in the isotope 136Xe using a monolithic liquid-Xe time-projection chamber (TPC) detector deployed at the Waste Isolation Pilot Plant WIPP mine in New Mexico, USA. It is filled with ~200kg of Xe enriched in 136Xe to more than 80%. The energy and position of each interaction in the detector are recorded, allowing a potential bb0n signal to be distinguished from backgrounds. So far no bb0n signal has been observed, resulting in a half-life limit of T1/2>1.1x1025 years (90% C.L.). McGill U. recently joined the EXO-200 collaboration, and I represent McGill on the EXO-200 collaboration board. I propose to establish a control center at McGill U. to train students and support remote data taking. It is planned and agreed on by the collaboration that EXO-200 takes data for a minimum of two years, improving the sensitivity to bb0n by more than a factor of 2. The development of nEXO, a next-generation Xe TPC, has started. This detector will consist of 5T of enriched liquid Xe. A potential location is the SNOLab facility in Sudbury. A unique feature in the search for bb0n in Xe is the possibility to extract and identify the 136Xe decay daughter, 136Ba. If a bb0n like event occurs inside the detector, the decay volume is extracted and probed for Ba. If Ba is found, the event can be identified as a bb-decay of 136Xe, while backgrounds that do not produce Ba are rejected. This Ba-tagging technique will greatly enhance the sensitivity of the detector compared to a conventional, background limited detector. Ba-tagging is possible in liquid and gaseous TPC detectors. Both possibilities are being pursued by the nEXO collaboration using several techniques. One possible technique is the Ba-extraction from a Xe gas into a vacuum environment. While at Stanford, Dan Fudenberg (PhD student at Stanford) and I developed a technique to extract ions from a noble gas at pressures up to 10 bar. I plan to move the central parts of this proof-of-principle experiment from Stanford to McGill. This is a unique system, and represents currently the leading edge of high-pressure ion-extraction studies. Once relocated, I will implement the remaining steps required for a practical gas tagging system with a ppb sensitivity. The experiment at McGill will provide a significant contribution to the Ba-tagging developments in the nEXO collaboration and has the potential to become a leading contribution to the experiment. It offer a unique opportunity to train students in cutting-edge technologies. I request funding to support the operation of EXO-200 and the development of a Ba-tagging technique in Xe gas. Furthermore, I will systematically investigate SiPMs for photon detection in nEXO.

寻找轻子数违反零中微子双β衰变(Bb0n)是当今粒子物理学面临的主要挑战之一。观测这种衰变需要中微子是马约拉纳粒子。EXO-200合作小组目前正在使用部署在美国新墨西哥州废物分离试点厂WIPP矿的整体式液体-Xe时间投影室(TPC)探测器来搜索同位素136Xe中的bb0n衰变。它是用~200公斤的Xe填充的，浓缩在136Xe中的Xe达到80%以上。探测器中每个相互作用的能量和位置都被记录下来，从而可以将潜在的bb0n信号与背景区分开来。到目前为止，还没有观察到bb0n信号，导致半衰期为T1/2&gt；1.1×1025年(90%C.L.)。麦吉尔大学最近加入了EXO-200协作组，我在EXO-200协作组代表麦吉尔。我建议在麦吉尔大学建立一个控制中心，以培训学生并支持远程数据获取。根据合作伙伴的计划和协议，EXO-200将获取至少两年的数据，将对bb0n的敏感度提高2倍以上。 下一代Xe TPC Nexo的开发已经开始。该探测器将由5T浓缩液Xe组成。一个潜在的地点是萨德伯里的SNOLab设施。寻找Xe中的bb0n的一个独特特征是有可能提取和鉴定136Xe衰变子体136Ba。如果探测器内部发生类似bb0n的事件，则提取衰变体积并探测是否存在bb。如果发现了Ba，则可以将该事件确定为136Xe的BB衰变，而不产生Ba的背景则被拒绝。与传统的本底受限探测器相比，这种加钡技术将极大地提高探测器的灵敏度。 BA标记在液体和气体TPC检测器中是可能的。Nexo的合作正在使用几种技术来探索这两种可能性。一种可能的技术是从Xe气体中提取钡到真空环境中。在斯坦福大学时，丹·富登伯格(斯坦福大学的博士生)和我开发了一种技术，可以在压力高达10巴的情况下从惰性气体中提取离子。我计划将这个原则证明实验的中心部分从斯坦福大学转移到麦吉尔大学。这是一个独特的系统，代表了目前高压离子提取研究的前沿。一旦搬迁，我将实施实际气体标签系统所需的其余步骤，并具有ppb灵敏度。麦吉尔的实验将为Nexo合作中的BaTaging开发做出重大贡献，并有可能成为该实验的主要贡献。它提供了一个独特的机会来培训学生的尖端技术。 我请求提供资金，支持EXO-200的运行和Xe气体中巴标记技术的开发。此外，我还将系统地研究用于Nexo中光子探测的SiPM。