Ultrasensitive Investigation of the Double Beta Decay Ge-76 using Large Crystals of Deep Mined Germanium (Physics)

该提案旨在继续支持 大六晶超低本底锗的研制 光谱仪，以及它在Homestake金矿的安装。 探测器将用于所有模式的灵敏搜索 锗-76的双β衰变 一个基本特征 由于污染物，检测器的背景降低。 原始污染物减少了三分之一以上 数量级。 新的背景来源也已 删除. 目前超低背景的数据 原型探测器已经与其他数据相结合， 4x 1023年的限制。无中微子双β衰变 锗-76，对应的中微子质量小于2.4eV 用壳模型计算核结构。 虽然 最近，圣巴巴拉/LBL已经超过了这个极限 小组，目前的探测器，这是特别深的开采， 宇宙成因放射性很低（低于0.2 计数/keV/yr/kg），将允许进一步减少， 极限 原型的低能量部分数据 被用来限制暗物质的质量和耦合 候选物质和DFS太阳轴子与 电子。 最后，一个异常的隆起被发现在 光谱的低背景原型，这是暗示 无中微子双β衰变， 无质量粒子 这种令人兴奋的可能性， 与其他锗-76实验证实或反驳 因为最好的仍然有更多的背景在一个关键的 区域的频谱，将在一个新的改进探索 实验

This proposal is for the continuation of support for development of a large 6 crystal ultralow background Ge spectrometer, and its installation in the Homestake goldmine. The detector will be used for a sensitive search for all modes of the double beta decay of Germanium-76. An essential feature of the detector is reduced background due to contaminants. Primordial contaminants have been reduced by more than three orders of magnitude. New sources of background have also been removed. The data from the present ultralow background prototype detectors have been combined with other data to place a limit of 4x1023yr. for the neutrinoless double beta-decay of Germanium-76, corresponding to a neutrino mass less than 2.4eV using the shell model nuclear structure calculations. Although this limit has recently been surpassed by the Santa Barbara/LBL group, the present detector, which was specially deep mined and is very low in cosmogenic radioactivity (below 0.2 counts/keV/yr/kg), will permit further reductions in that limit. The low energy portion of the data from the prototype was used to place limits on the mass and couplings of dark matter candidates and on the coupling of DFS solar axions to electrons. Finally, an anomalous bump was discovered in the spectrum of the low background prototype, which was suggestive of neutrinoless double beta-decay with a massless or almost massless particle. This exciting possibility, which cannot be confirmed or refuted with other Germanium-76 experiments because the best ones still have more background in a critical region of the spectrum, will be explored in a new improved experiment.