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摘要
本文基于 CDEX-10 实验中 C10B-Ge1 高纯锗探测器的 205.4 kg·day 曝光数据，首次利用锗原子电子靶搜寻亚 MeV 费米子暗物质吸收过程 χ + e⁻ → ν + e⁻。该分析采用 160 eVee 的低能阈值，并使用 0.16–2.16 keVee 能区的实验能谱，对 0.1–10 keV/c² 质量范围内的暗物质信号进行检验。理论信号模型考虑矢量型与轴矢量型有效相互作用算符，锗原子按孤立原子近似处理，并主要采用 K、L、M 壳层核心电子贡献，从而给出相对保守的预期信号谱。数据分析中，背景模型包括宇宙成因放射性同位素的 L/M 壳层 X 射线峰以及高能 γ 射线康普顿散射连续本底，并通过 χ² 拟合结合探测效率和本底强度的不确定性进行约束。实验结果未发现显著超出本底的暗物质信号，因此采用 Feldman-Cousins 方法给出 90% 置信水平上限。在 mχ = 5 keV/c² 处，矢量相互作用截面上限为 6.8 × 10⁻⁴⁶ cm²，轴矢量相互作用截面上限为 2.3 × 10⁻⁴⁶ cm²。该结果在 10 keV/c² 以下质量区间给出了新的直接探测限制，并将费米子暗物质电子吸收过程的直接探测灵敏质量推进到目前最低范围。
Abstract
This work reports the first search for sub-MeV fermionic dark matter absorption on electron targets in germanium using 205.4 kg·day of data from the CDEX-10 C10B-Ge1 high-purity germanium detector. Benefiting from a low analysis threshold of 160 eVee, the study probes fermionic dark matter in the mass range of 0.1–10 keV/c² through the absorption process χ + e⁻ → ν + e⁻. Signal models are constructed for vector and axial-vector effective interaction operators. Germanium atoms are treated as isolated atoms, and only the core-electron contributions from the K, L, and M shells are included, leading to conservative signal predictions. The analysis uses the measured spectrum from 0.16 to 2.16 keVee and performs a χ² fit including detector efficiency uncertainties and background components from cosmogenic isotope L/M-shell x-ray peaks and Compton scattering of high-energy γ rays. No significant excess above the expected background is observed. Upper limits at 90% confidence level are therefore derived using the Feldman-Cousins method. At a dark matter mass of 5 keV/c², the obtained limits on the interaction cross section are 6.8 × 10⁻⁴⁶ cm² for the vector operator and 2.3 × 10⁻⁴⁶ cm² for the axial-vector operator. These results provide new constraints below 10 keV/c² and reach the lowest fermionic dark matter mass region explored so far by direct detection experiments.
| 关键词 | 费米子暗物质，电子吸收，直接探测实验，高纯锗探测器 |
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| Keywords | fermionic Dark Matter, electron absorption, direct detection experiment, high purity germanium detector |
