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存在一种与希格斯场无关的新的质量生成机制，并有助于揭示我们所看到的物质支配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衰变产生的单个Ba离子。 之前的0nbb搜索一直是后台受限的。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合作进行了一次密集的R演示，使用放射性离子从LXE中高效地收集离子[在Carleton大学] 使用射频离子漏斗和多次反射飞行时间质谱仪向低压分析室演示有效的离子提取[在麦吉尔大学] 设计、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] 演示巴-136离子与其他自然产生的钡同位素的光学辨别[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，可以完全消除残留的放射性背景，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.