基于荧光双色传感器的无本底无中微子双β衰变实验
Towards a background-free neutrinoless double beta decay experiment based on a fluorescent bicolor sensor
摘要：
寻找无中微子双β衰变（$β\beta0ν$）是确定中微子是否是其自身反粒子的唯一可行方法。由于中微子质量很小，预计$β\beta0ν$的寿命至少比天然放射性链的噪声小10个数量级。$β\beta0ν$衰变的阳性鉴定最终需要找到放射性背景不能模拟的信号。这个信号可能是在衰变中观察到的子原子，因为没有已知的背景过程诱导Z+2变换。特别是，可以通过检测双电离的子原子Ba $^{2+}$来确定Xe-136的$β\beta0ν$衰变。这种检测可以通过由单层分子指示剂制成的传感器来实现。Ba $^{2+}$将被传感器中的一个分子捕获，随后通过用激光系统反复询问的强荧光响应来揭示单个螯合指示剂的存在。在这里，我们描述了一种荧光双色指示剂，强烈结合到Ba $^{2+}$，并发出非常明亮的光，当在干燥介质中螯合时，将其发射颜色从绿色变为蓝色，从而允许明确识别传感器中的单个钡原子，并允许在气室中对$β\beta0ν$的衰变进行阳性识别，这可能导致无背景实验。
英文摘要：
Searching for neutrinoless double beta decays ($β\beta0ν$) is the only practical way to establish if the neutrinos are their own antiparticles. Due to the smallness of neutrino masses, the lifetime of $β\beta0ν$ is expected to be at least ten orders of magnitude smaller than the noise associated with the natural radioactive chains. A positive identification of $β\beta0ν$ decays requires, ultimately, finding a signal that cannot be mimicked by radioactive backgrounds. This signal could be the observation of the daughter atom in the decay, since no known background processes induce a Z+2 transformation. In particular, the $β\beta0ν$ decay of Xe-136 could be established by detecting the doubly ionised daughter atom, Ba$^{2+}$. Such a detection could be achieved via a sensor made of a monolayer of molecular indicators. The Ba$^{2+}$ would be captured by one of the molecules in the sensor, and the presence of the single chelated indicator would be subsequently revealed by a strong fluorescent response from repeated interrogation with a laser system. Here we describe a fluorescent bicolor indicator that binds strongly to Ba$^{2+}$ and shines very brightly, shifting its emission colour from green to blue when chelated in dry medium, thus allowing the unambiguous identification of single barium atoms in the sensor, and permitting a positive identification of the $β\beta0ν$ decay of Xe-136 in a gas chamber, that could led to a background-free experiment.
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