运动学边界处的暗物质：解释LZ合作组的248 keV核反冲候选事例
Dark Matter at the Kinematic Edge: Interpreting the 248 keV LZ Nuclear-Recoil Candidate
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中文总结 AI 辅助
本研究结合LZ合作组观测的248 keV核反冲候选事例，探究暗物质模型能否解释该事例，发现吸热散射或带特定参数的热赝狄拉克费米子、热希格斯诺模型可实现，且该解释可通过伽马射线信号检验。
中文摘要 AI 辅助
LZ（LUX-ZEPLIN）合作组近期报告，在2.84吨-年的曝光量中观测到一个与248 keV核反冲相符的事例，其局域最大显著性为3.4σ，全局显著性为2.6σ。我们探究该高能事例所青睐的暗物质（DM）-核子相互作用是否可源自粒子暗物质模型，此类模型需同时再现观测到的遗迹丰度并满足间接探测约束。利用已发表的LZ效率与算符显著性，我们表明弹性自旋无关（SI）散射难以解释孤立的高能反冲，因其能谱集中在低能区；而弹性自旋相关（SD）O₄散射仍具可行性。吸热散射则可自然压低低能事例率，并将反冲能谱移至观测能量附近，带非对角矢量相互作用的热赝狄拉克费米子为该机制提供了简单实现。对于m_χ≈1 TeV，遗迹密度要求预测σ_N≈6.5×10⁻⁴³ cm²，而质量分裂δ≈297 keV可将反冲能谱移至LZ事例区域。现今的间接探测信号可被强烈压低，因为退耦主要通过共湮灭发生，激发态在晚期被耗尽。热希格斯诺则提供了更具预测性的实现：其遗迹丰度将质量固定在1.1 TeV附近，而要再现该事例需质量分裂δ≈371 keV。该解释可通过相关伽马射线线信号进行检验。总体而言，结合直接探测、遗迹密度与间接探测，可显著限制LZ事例的可行解释，并为未来搜寻提供具体目标。
英文摘要
The LUX-ZEPLIN (LZ) Collaboration recently reported one event consistent with a $248$ keV nuclear recoil in a $2.84$ tonne-year exposure, with a maximum local significance of $3.4σ$ and a global significance of $2.6σ$. We investigate whether the dark matter (DM)--nucleon interactions favored by this high-energy event can arise from particle DM models that simultaneously reproduce the observed relic abundance and satisfy indirect-detection constraints. Using the published LZ efficiency and operator significances, we show that elastic spin-independent (SI) scattering poorly explains an isolated high-energy recoil because its spectrum is concentrated at lower energies, whereas elastic spin-dependent (SD) $\mathcal{O}_4$ scattering remains viable. Endothermic scattering instead naturally suppresses the low-energy rate and shifts the recoil spectrum toward the observed energy. A thermal pseudo-Dirac fermion with an off-diagonal vector interaction provides a simple realization of this mechanism. For $m_χ\simeq1$ TeV, the relic-density requirement predicts $σ_N\simeq6.5\times10^{-43}\,\mathrm{cm}^2$, while a splitting $δ\simeq297$ keV shifts the recoil spectrum into the LZ event region. Present-day indirect-detection signals can be strongly suppressed because freeze-out proceeds mainly through coannihilation, while the excited state is depleted at late times. A thermal Higgsino provides a more predictive realization: its relic abundance fixes the mass near $1.1$ TeV, while a splitting $δ\simeq 377$ keV is required to reproduce the event. This interpretation is testable through the associated gamma-ray line signal. Overall, combining direct detection, relic density, and indirect detection significantly restricts the viable interpretations of the LZ event and provides concrete targets for future searches.
发表机构
- Istituto Nazionale di Fisica Nucleare, Sezione di Torino（意大利国家核物理研究所都灵分部）
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