We discuss several low-energy backgrounds to sub-GeV dark-matter searches, which arise from high-energy particles of cosmic or radioactive origin that interact with detector materials. We focus, in particular, on Cherenkov radiation, transition radiation, and luminescence or phonons from electron-hole pair recombination and show that these processes are an important source of backgrounds at both current and planned detectors. We perform detailed analyses of these backgrounds at several existing and proposed experiments based on a wide variety of detection strategies and levels of shielding. We find that a large fraction of the observed single-electron events in the SENSEI 2020 run originate from Cherenkov photons generated by high-energy events in the Skipper charge coupled device and from recombination photons generated in a phosphorus-doped layer of the same instrument. In a SuperCDMS HVeV 2020 run, Cherenkov photons produced in printed-circuit boards located near the sensor likely explain the origin of most of the events containing 2–6 electrons. At SuperCDMS SNOLAB, radioactive contaminants inside the Cirlex located inside or on the copper side walls of their detectors produce many Cherenkov photons, which could dominate the low-energy backgrounds. For the EDELWEISS experiment, Cherenkov or luminescence backgrounds are subdominant to their observed event rate but could still limit the sensitivity of their future searches. We also point out that Cherenkov radiation, transition radiation, and recombination could be a significant source of backgrounds at future experiments aiming to detect dark matter via scintillation or phonon signals. We also discuss the implications of our results for the development of superconducting qubits and low-threshold searches for coherent neutrino scattering. Fortunately, several design strategies to mitigate these backgrounds can be implemented, such as minimizing nonconductive materials near the target, implementing active and passive shielding, and using multiple nearby detectors.

中文翻译：

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低阈值暗物质和中微子探测器中低能事件的来源

我们讨论了亚 GeV 暗物质搜索的几种低能背景，这些背景来自与探测器材料相互作用的宇宙或放射性来源的高能粒子。我们特别关注切伦科夫辐射、跃迁辐射和来自电子-空穴对重组的发光或声子，并表明这些过程是当前和计划中的探测器的重要背景来源。我们基于多种检测策略和屏蔽级别，在几个现有和提议的实验中对这些背景进行了详细分析。我们发现，在 SENSEI 2020 运行中观察到的大部分单电子事件源自 Skipper 电荷耦合器件中的高能事件产生的切伦科夫光子以及同一仪器的磷掺杂层中产生的复合光子。在 SuperCDMS HVeV 2020 运行中，位于传感器附近的印刷电路板中产生的切伦科夫光子可能解释了大多数包含 2-6 个电子的事件的起源。在 SuperCDMS SNOLAB，位于探测器内部或铜侧壁上的 Cirlex 内部的放射性污染物会产生许多切伦科夫光子，这些光子可能会主导低能背景。对于 EDELWEISS 实验，Cherenkov 或发光背景在其观察到的事件发生率中处于次要地位，但仍可能限制其未来搜索的灵敏度。我们还指出，在未来旨在通过闪烁或声子信号检测暗物质的实验中，切伦科夫辐射、跃迁辐射和重组可能是重要的背景来源。我们还讨论了我们的结果对超导量子比特的发展和相干中微子散射的低阈值搜索的影响。幸运的是，可以实施多种设计策略来减轻这些背景，例如尽量减少目标附近的非导电材料、实施主动和被动屏蔽以及使用多个附近的探测器。我们还讨论了我们的结果对超导量子比特的发展和相干中微子散射的低阈值搜索的影响。幸运的是，可以实施多种设计策略来减轻这些背景，例如尽量减少目标附近的非导电材料、实施主动和被动屏蔽以及使用多个附近的探测器。我们还讨论了我们的结果对超导量子比特的发展和相干中微子散射的低阈值搜索的影响。幸运的是，可以实施多种设计策略来减轻这些背景，例如尽量减少目标附近的非导电材料、实施主动和被动屏蔽以及使用多个附近的探测器。