Frontier Neutrino Physics: Ba ion tagging

中微子振荡实验已经证明了中微子是有质量的，但它们的绝对规模不能从这样的测量中确定。无中微子双β衰变（0 nbb）实验能够探测中微子是否是马约拉纳粒子，帮助确定中微子质谱并探索标准模型之外的物理学。对这种轻子数违反过程的观察将证明存在一种与希格斯场无关的新的质量产生机制，并揭示了我们所目睹的物质主导宇宙的原始物理学。 下一代0 nbb实验需要吨级的活动质量和极低的本底。nEXO合作项目提出了一个5吨重的液体氙（LXe）时间投影室，该室对氙-136 0 nbb衰变的半衰期具有足够的灵敏度，能够探索参数空间的反向质量等级区域。为了进一步达到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β-136的双β衰变独特产生的单个Ba离子。 以前的0 nbb搜索是背景有限的。用Ba离子标记，可以完全排除残留的放射性背景。来自允许的2nbb衰变的高能量尾部的事件只能通过优异的探测器能量分辨率来减轻。nEXO合作进行了一项强烈的R演示，使用放射性离子从Lion收集有效的离子[在卡尔顿大学] 使用RF离子漏斗和多反射飞行时间质谱仪证明了对低压分析室的有效离子提取[在麦吉尔大学] 设计、优化和构建具有离子冷却和聚束能力的高信噪比线性Paul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别[在卡尔顿大学] Ba离子标记技术的改进仍然非常具有挑战性，但该方法提供了一个独特的机会，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与正常质量等级相关的所有相关参数空间。鉴于该计划的跨学科性质，我们希望吸引许多研究生，并为培训技术人员和博士后研究员提供很好的机会。

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.