Observation of the neutrinoless double β decay is the only practical way to establish that neutrinos are their own antiparticles 1 . Because of the small masses of neutrinos, the lifetime of neutrinoless double β decay is expected to be at least ten orders of magnitude greater than the typical lifetimes of natural radioactive chains, which can mimic the experimental signature of neutrinoless double β decay 2 . The most robust identification of neutrinoless double β decay requires the definition of a signature signal—such as the observation of the daughter atom in the decay—that cannot be generated by radioactive backgrounds, as well as excellent energy resolution. In particular, the neutrinoless double β decay of 136 Xe could be established by detecting the daughter atom, 136 Ba 2+ , in its doubly ionized state 3 – 8 . Here we demonstrate an important step towards a ‘barium-tagging’ experiment, which identifies double β decay through the detection of a single Ba 2+ ion. We propose a fluorescent bicolour indicator as the core of a sensor that can detect single Ba 2+ ions in a high-pressure xenon gas detector. In a sensor made of a monolayer of such indicators, the Ba 2+ dication would be captured by one of the molecules and generate a Ba 2+ -coordinated species with distinct photophysical properties. The presence of such a single Ba 2+ -coordinated indicator would be revealed by its response to repeated interrogation with a laser system, enabling the development of a sensor able to detect single Ba 2+ ions in high-pressure xenon gas detectors for barium-tagging experiments. A fluorescent bicolour sensor is proposed as the basis of a barium-tagging technique for the detection of neutrinoless double β decay in xenon gas experiments.

中文翻译：

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用于低背景中微子双 β 衰变实验的荧光双色传感器

观察中微子双 β 衰变是确定中微子是它们自己的反粒子 1 的唯一实用方法。由于中微子的质量很小，无中微子双 β 衰变的寿命预计比天然放射性链的典型寿命至少大十个数量级，这可以模拟无中微子双 β 衰变 2 的实验特征。对无中微子双 β 衰变最可靠的识别需要定义特征信号——例如观察衰变中的子原子——这是放射性背景无法产生的，以及出色的能量分辨率。特别是，136 Xe 的无中微子双 β 衰变可以通过检测处于双电离态 3 – 8 的子原子 136 Ba 2+ 来建立。在这里，我们展示了朝着“钡标记”实验迈出的重要一步，该实验通过检测单个 Ba 2+ 离子来识别双 β 衰变。我们提出了一种荧光双色指示剂作为传感器的核心，可以在高压氙气检测器中检测单个 Ba 2+ 离子。在由这种指示剂的单层制成的传感器中，Ba 2+ 阳离子将被其中一个分子捕获并产生具有不同光物理特性的Ba 2+ 配位物质。这种单一的 Ba 2+ 配位指示剂的存在将通过其对激光系统重复询问的响应来揭示，从而能够开发出一种能够在用于钡的高压氙气检测器中检测单个 Ba 2+ 离子的传感器。标记实验。