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型 6 晶体超低本底 Ge 光谱仪的开发及其在 Homestake 金矿的安装。 该探测器将用于灵敏搜索锗 76 双 β 衰变的所有模式。 检测器的一个基本功能是减少污染物造成的背景。 原始污染物已减少三个数量级以上。 新的背景来源也已被删除。 目前超低背景原型探测器的数据已与其他数据相结合，设定了 4x1023 年的限制。对于Ge-76的无中微子双β衰变，使用壳模型核结构计算对应的中微子质量小于2.4eV。 尽管圣巴巴拉/LBL小组最近已经超越了这一限制，但目前的探测器是专门深部开采的，宇宙源放射性非常低（低于0.2计数/keV/年/千克），将允许进一​​步降低该限制。 原型数据的低能量部分用于限制候选暗物质的质量和耦合以及 DFS 太阳轴子与电子的耦合。 最后，在低背景原型的光谱中发现了一个异常凸起，这表明存在无质量或几乎无质量粒子的无中微子双β衰变。 这种令人兴奋的可能性无法用其他锗 76 实验来证实或反驳，因为最好的实验在光谱的关键区域仍然有更多的背景，将在一项新的改进实验中进行探索。

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.