在高通量反应堆中通过束管探测氢原子的自由中子束缚β衰变的首次测量
Towards a first measurement of the free neutron bound beta decay detecting hydrogen atoms at a throughgoing beamtube in a high flux reactor
摘要：
除了常见的中子$n\rightarrow p e^-\overline{ν_e}$的三体衰变之外，还应该存在一个有效的2体子集，其中电子和质子形成具有良好定义的总动量、总自旋和磁量子数的氢束缚态。这个束缚系统的原子光谱分析可以揭示潜在的弱相互作用的细节，因为它反映了所有出射粒子的螺旋度分布。因此，它携带的信息是独一无二的，而解开这些信息的实验类似于60多年前进行的戈德哈伯实验。所提出的实验将搜索具有326 eV动能的单能亚稳态BoBH原子，其产生于高通量反应堆的贯穿束管的中心（例如，在PIK反应堆，Gatchina）。虽然需要完整的光谱信息来揭示新的物理学，但我们的首要目标是证明这种衰变的发生并了解背景。检测的关键是识别在许多氢原子的环境中以约1 $\rm{s}^{-1}$的速率出现的氢原子的单色线，然而具有约室温的热分布。本文讨论了速度（能量）滤波的两种情况。第一种是建立在一个纯电动斩波器系统上的，在这个系统中，亚稳态的氢原子被淬灭到它们的基态，因此大部分保持在不可检测的状态。该斩波器系统采用快速可切换的Bradbury Nielsen门。第二种方法利用了一个强烈的能量依赖的电荷交换过程，亚稳态氢拿起一个电子，同时穿越充满氩气的气体电池，把它变成可操纵的带电氢。氢气的最终检测通过多通道板（MCP）检测器进行。
英文摘要：
In addition to the common 3-body decay of the neutron $n\rightarrow p e^-\overline{ν_e}$ there should exist an effective 2-body subset with the electron and proton forming a Hydrogen bound state with well defined total momentum, total spin and magnetic quantum numbers. The atomic spectroscopic analysis of this bound system can reveal details about the underlying weak interaction as it mirrors the helicity distributions of all outgoing particles. Thus, it is unique in the information it carries, and an experiment unravelling this information is an analogue to the Goldhaber experiment performed more than 60 years ago. The proposed experiment will search for monoenergetic metastable BoB H atoms with 326 eV kinetic energy, which are generated at the center of a throughgoing beamtube of a high-flux reactor (e.g., at the PIK reactor, Gatchina). Although full spectroscopic information is needed to possibly reveal new physics our first aim is to prove the occurrence of this decay and learn about backgrounds. Key to the detection is the identification of a monoerergtic line of hydrogen atoms occurring at a rate of about 1 $\rm{s}^{-1}$ in the environment of many hydrogen atoms, however having a thermal distribution of about room temperature. Two scenarios for velocity (energy) filtering are discussed in this paper. The first builds on an purely electric chopper system, in which metastable hydrogen atoms are quenched to their ground state and thus remain mostly undetectable. This chopper system employs fast switchable Bradbury Nielsen gates. The second method exploits a strongly energy dependent charge exchange process of metastable hydrogen picking up an electron while traversing an argon filled gas cell, turning it into manipulable charged hydrogen. The final detection of hydrogen occurs through multichannel plate (MCP) detector.
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