Fixed-target experiments using primary electron beams can be powerful discovery tools for light dark matter in the sub-GeV mass range. The Light Dark Matter eXperiment (LDMX) is designed to measure missing momentum in high-rate electron fixed-target reactions with beam energies of 4 GeV to 16 GeV. A prerequisite for achieving several important sensitivity milestones is the capability to efficiently reject backgrounds associated with few-GeV bremsstrahlung, by twelve orders of magnitude, while maintaining high efficiency for signal. The primary challenge arises from events with photo-nuclear reactions faking the missing-momentum property of a dark matter signal. We present a methodology developed for the LDMX detector concept that is capable of the required rejection. By employing a detailed GEANT4-based model of the detector response, we demonstrate that the sampling calorimetry proposed for LDMX can achieve better than $10^{-13}$ rejection of few-GeV photons. This suggests that the luminosity-limited sensitivity of LDMX can be realized at 4 GeV and higher beam energies.

中文翻译：

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光暗物质实验的高效光子否决权

使用初级电子束的固定目标实验可以成为亚 GeV 质量范围内轻暗物质的强大发现工具。光暗物质实验 (LDMX) 旨在测量束能量为 4 GeV 至 16 GeV 的高速率电子固定目标反应中的缺失动量。实现几个重要的灵敏度里程碑的先决条件是能够有效地将与少量 GeV 韧致辐射相关的背景抑制 12 个数量级，同时保持信号的高效率。主要挑战来自伪造暗物质信号缺失动量特性的光核反应事件。我们提出了一种为 LDMX 检测器概念开发的方法，该方法能够实现所需的抑制。通过采用基于 GEANT4 的详细探测器响应模型，我们证明了为 LDMX 提出的采样量热法可以实现优于 $10^{-13}$ 的几个 GeV 光子的拒绝。这表明 LDMX 的光度限制灵敏度可以在 4 GeV 和更高的光束能量下实现。