Background-free search for neutrinoless double-β decay of 76Ge with GERDA
Background-free search for neutrinoless double-β decay of 76Ge with GERDA
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DOI：
10.1038/nature21717
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发表时间：
2017-04-06
期刊：
影响因子：
64.8
通讯作者：
Zuzel, G.
中科院分区：
文献类型：
--
作者：
Agostini, M.;Allardt, M.;Zuzel, G.
粒子物理学标准模型的许多扩展解释了在我们的宇宙中，中微子是自己的反粒子，从而解释了物质相对于反物质的优势。这将意味着无中微子双β衰变的存在，这是一种极其罕见的违反轻子数的放射性衰变过程，其探测需要最大限度的背景抑制。在旨在探测这种衰变的项目中，Gerda的合作正在通过操作液态Ar中的裸露探测器来寻找Ge-76的无中微子双β衰变，探测器由富含Ge-76组分的Ge制成。在完成了第一阶段的数据采集后，我们最近启动了第二阶段。在这里，我们报告在Gerda第二阶段，我们已经达到了大约10(-3)个kev(-1)kg(-1)yr(-1)的本底水平。这意味着实验是无背景的，即使当曝光增加到设计水平时也是如此。这是通过使用主动否决系统、优越的锗探测器能量分辨率和改进我们的新探测器的背景识别来实现的。当第一阶段和第二阶段的数据结合在一起时，没有发现无中微子双β衰变的信号，我们在90%的置信度水平下推导出了5.3×10(25)年的下限半衰期。我们4.0x10(25)年的半衰期灵敏度与使用大得多的同位素质量的最好的实验相竞争。对无中微子双β衰变的基本无背景搜索的可能性将促进具有灵敏度水平的更大规模的锗实验，这将使我们更接近于澄清中微子是否是它们自己的反粒子。
Many extensions of the Standard Model of particle physics explain the dominance of matter over antimatter in our Universe by neutrinos being their own antiparticles. This would imply the existence of neutrinoless double-beta decay, which is an extremely rare lepton-number-violating radioactive decay process whose detection requires the utmost background suppression. Among the programmes that aim to detect this decay, the GERDA Collaboration is searching for neutrinoless double-beta decay of Ge-76 by operating bare detectors, made of germanium with an enriched Ge-76 fraction, in liquid argon. After having completed Phase I of data taking, we have recently launched Phase II. Here we report that in GERDA Phase II we have achieved a background level of approximately 10(-3) counts keV(-1) kg(-1) yr(-1). This implies that the experiment is background-free, even when increasing the exposure up to design level. This is achieved by use of an active veto system, superior germanium detector energy resolution and improved background recognition of our new detectors. No signal of neutrinoless double-beta decay was found when Phase I and Phase II data were combined, and we deduce a lower-limit half-life of 5.3 x 10(25) years at the 90 per cent confidence level. Our half-life sensitivity of 4.0 x 10(25) years is competitive with the best experiments that use a substantially larger isotope mass. The potential of an essentially background-free search for neutrinoless double-beta decay will facilitate a larger germanium experiment with sensitivity levels that will bring us closer to clarifying whether neutrinos are their own antiparticles.