Frontier Neutrino Physics: Ba ion tagging

中微子振荡实验已经证明，中微子质量很大，但无法从这种测量中确定其绝对规模。无中微子双β衰变(0NBB)实验能够探测中微子是否是Majorana粒子，帮助确定中微子质量谱，并探索标准模型以外的物理。对轻子数破坏过程的观察将证明一种与希格斯场无关的新质量生成机制的存在，并揭示我们所看到的物质主导的宇宙的原始物理机制。*下一代0nbb实验需要吨级的活动质量和极低的本底。Nexo的合作提出了一个5吨重的液体氙气(LXE)时间投影室，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置质量等级区域。为了更进一步并达到对正常谱系的最终灵敏度，我们建议探索一种复杂的背景拒绝技术，该技术要求探测由Xe-136的双β衰变唯一产生的单个Ba离子。*以前的0nbb搜索一直受到背景限制。用钡离子标记，可以完全排除残留的放射性本底。来自允许的2NBb衰变的高能尾部的事件只能通过出色的探测器能量分辨率来缓解。Nexo合作使用放射性离子从LXE进行了密集的R演示高效离子收集[在Carleton大学]*演示了使用RF离子漏斗和多反射飞行时间质谱仪[在McGill大学]*设计高效地将离子提取到低压分析室，优化和建造具有离子冷却和聚束能力的高信噪比线性Paul陷阱[在TRIUMF]*展示了BA-136离子与其他自然发生的Ba2同位素的光学分辨[在Carleton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，可以完全消除剩余的放射性背景，它将使未来的吨级实验能够扫描与正常质量等级相关的所有相关参数空间。鉴于该项目的跨学科性质，我们预计将吸引许多研究生，并为培训技术人员和博士后研究员提供良好的机会。

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.**