Phase I Loading of 130Te in SNO+

寻找中微子双β衰变被认为是当今粒子物理研究中最优先的领域之一。对这一违反轻子数过程的观察将建立中微子的绝对质量尺度，为大统一提供洞见，并为轻子发生模型提供依据。SNO+所采用的特殊方法是将一种候选同位素（最初为150Nd）装载在一个大体积的液体闪烁体中。虽然这种实验的能量分辨率不如固态设备，但高纯度液体的大自屏蔽体积允许在低背景水平下实现非常大量的同位素。此外，易于修改液体结构的能力为探测任何候选信号提供了显着优势，并且易于实现对纯化和装载的进一步改进。在过去的18个月里，由Biller和Chen（在加拿大女王大学休假期间）在牛津大学发起的工作取得了重大进展，他们确定了一种更有利的同位素，可以加载到液体闪烁体中，以获得对中微子双β衰变的高灵敏度。随后，布鲁克海文国家实验室的同事开发了一种新的金属装载技术和纯化方法，并于2013年3月完成了对牛津/女王提议的彻底的独立内部审查，该合作决定继续部署130Te作为双β衰变的主要目标同位素。我们计划在2014年开始在探测器中初始装载约800kg的130Te。我们的预测是，即使在这个阶段，SNO+在接近反向中微子质量层次顶端的区域，至少可以达到与该领域领先的实验相媲美的灵敏度。这种同位素数量的选择是基于经济考虑和与预期的第二阶段相关的规模的适当性，并不代表该方法的技术限制。因此，在这一阶段的成功演示和持续研发工作的等待结果之后，我们的目标是尽快将装载量增加到多吨规模（可能最早在2015年为此寻求初始资金）。这将使我们远远领先于任何其他实验，更重要的是，这将使我们达到接近反向中微子质量等级底层的灵敏度，并在感兴趣的区域的中心有发现的潜力。这项建议要求提供支助，以支付与这一努力第一阶段有关的额外费用。

The search for neutrinoless double beta decay is recognized as one of the highest priority areas of particle physics research today. The observation of this Lepton number-violating process would establish the absolute mass scale of neutrinos, provide insight into Grand Unification and lend weight to models of leptogenesis. The particular approach taken by SNO+ involves loading a large target volume of liquid scintillator with a candidate isotope, originally 150Nd. While the energy resolution of such an experiment is not as good as for solid-state devices, the large self-shielding volumes of high purity liquids allow the potential for realising very large quantities of isotope with low levels of background. Further, the ability to easily modify the liquid configuration offers a significant advantage for probing any candidate signal and readily allowing the implementation of further improvements to purification and loading. Significant developments have taken place over the last 18 months, initiated by work at Oxford by Biller and Chen (while on sabbatical from Queen's University, Canada), which have led to the identification of a more favourable isotope to load into the liquid scintillator for high sensitivity to neutrinoless double beta decay. Following the subsequent development of a new metal loading technique and purification method by colleagues at Brookhaven National Laboratory, and a thorough independent internal review of the Oxford/Queen's proposal completed in March 2013, the collaboration has decided to pursue the deployment of 130Te as the primary target isotope for double beta decay. We are planning for an initial loading corresponding to ~800kg of 130Te in the detector, to begin in 2014. Our projections are that, even at this stage, SNO+ would attain sensitivity at least comparable to that of the leading proposed experiments in the field, in the region near the top of the inverted neutrino mass hierarchy. This quantity of isotope was chosen based on economic considerations and the appropriateness of scale relevant to lead to an anticipated secondary phase, and does not represent a technical limitation of the approach. Thus, following a successful demonstration of this phase and pending results from the continuing R&D effort, we would then aim to increase the loading to the multi-tonne scale as soon as is feasible (potentially seeking initial funding for this as early as 2015). This would put us well ahead of any other experiment and, more importantly, would let us achieve a sensitivity that reaches to near the bottom of the inverted neutrino mass hierarchy, with discovery potential in heart of the region of interest. This proposal requests support to contribute to the additional costs associated with the first phase of this endeavour.