Frontier Neutrino Physics: Ba ion tagging

中微子振荡实验已经证明了中微子是巨大的，但是它们的绝对尺度不能通过这样的测量来确定。中微子双衰变（0nbb）实验能够探测中微子是否是马约拉纳粒子，帮助确定中微子的质谱，并探索标准模型之外的物理。对这个轻子数违反过程的观察将证明一种与希格斯场无关的新的质量生成机制的存在，并揭示了我们正在目睹的物质主导宇宙的原始物理学。***下一代0nbb实验需要吨级有效质量和极低背景。nEXO合作正在提出一个5吨的液态氙（LXe）时间投影室，它对Xe-136 0nbb衰变的半衰期具有足够的灵敏度，能够探索参数空间的倒质量层次区域。为了进一步达到对正常层次的最终灵敏度，我们建议探索一种复杂的背景抑制技术，该技术要求检测由Xe-136的双β衰变独特产生的单个Ba离子。***以前的0nbb搜索已被背景限制。使用钡离子标记，可以完全拒绝残余放射性本底。来自允许的2nbb衰变的高能尾的事件只能通过出色的探测器能量分辨率来减轻。nEXO合作项目利用放射性离子从LXe中高效收集R离子[在卡尔顿大学]***利用RF离子漏斗和多反射飞行时间质谱仪设计，在低压分析室中高效提取离子[在麦吉尔大学]***。优化和构建具有离子冷却和聚束能力的高信噪比线性保罗阱[在TRIUMF]***演示Ba-136离子与其他天然存在的钡同位素的光学区分[在卡尔顿大学]***改进Ba离子标记技术仍然非常具有挑战性，但该方法提供了一个独特的机会来完全消除残留的放射性背景，它将允许未来的吨级实验扫描所有的与标准质量层次相关联的相关参数空间。鉴于该项目的跨学科性质，我们希望吸引许多研究生，并为培训技术人员和博士后提供良好的机会

Neutrino oscillation experiments have demonstrated that neutrinos are massive but their absolute scale cannot be established from such measurements. Neutrinoless double beta decay (0nbb) experiments are able to probe whether neutrinos are Majorana particles, help determine the neutrino mass spectrum and explore physics beyond the Standard Model. The observation of this lepton number violating process will demonstrate the existence of a new mass generation mechanism unrelated to the Higgs field and shed light on the primordial physics responsible for the matter dominated universe that we are witnessing.***The next-generation 0nbb experiments require tonne-scale active mass and extreme low background. The nEXO collaboration is proposing a 5-tonne liquid xenon (LXe) time projection chamber with sufficient sensitivity to the half-life of Xe-136 0nbb decay to be able to explore the inverted mass hierarchy region of the parameter space. To go further and reach the ultimate sensitivity to the normal hierarchy, we propose to explore a sophisticated technique for background rejection which calls for the detection of the single Ba ion produced uniquely by the double beta decay of Xe-136.***Previous 0nbb searches have been background limited. With Ba ion tagging, the residual radioactive background can be completely rejected. Events from the high energy tail of the allowed 2nbb decay can only be mitigated by excellent detector energy resolution. The nEXO collaboration conducts an intense R demonstrate efficient ion collection from LXe using radioactive ions [at Carleton university]*** demonstrate efficient ion extraction to a low-pressure analysis chamber using a RF ion funnel and a multi-reflection time-of-flight mass spectrometer [at McGill university]*** design, optimize and construct a high signal-to-noise ratio linear Paul trap with ion cooling and bunching capabilities [at TRIUMF]*** demonstrate optical discrimination of the Ba-136 ion against other natural occurring barium isotopes [at Carleton university]***The refinement of the Ba ion tagging technique remains very challenging but the method provides a unique opportunity to fully eliminate the residual radioactive backgrounds and it will allow a future tonne-scale experiment to scan all the relevant parameter space associated with the normal mass hierarchy. Given the interdisciplinary nature of the program, we expect to attract many graduate students and provide great opportunities for training technicians and post-doctoral fellows.**