AI 中文总结
InDEx实验通过分析超热$C_2H_2F_4$靶的电子反冲信号，将暗物质探测范围扩展至亚GeV级（低至约10 MeV），提升了对轻子耦合暗物质的探测灵敏度。
AI 中文摘要
印度暗物质搜寻实验（InDEx）在贾杜古达地下科学实验室（JUSL）运行以四氟乙烷（$\boldsymbol{\rm C_2H_2F_4}$）为活性靶的超热液滴探测器，迄今仅在靶对电子反冲不敏感的工作温度下通过核反冲探测暗物质（DM）。本研究考虑6个工作温度：$T=45$–$70^\boldsymbol{\rm \bullet C}$，步长为$5^\boldsymbol{\rm \bullet C}$，对应的Seitz阈值范围从$0.61\boldsymbol{\rm keV}$降至$26.8\boldsymbol{\rm eV}$；采用孤立原子近似，通过Roothaan-Hartree-Fock波函数计算$\boldsymbol{\rm C_2H_2F_4}$靶的电离响应；在零本底假设下，针对$10^3\boldsymbol{\rm kg \bullet days}$的基准曝光量，分别在重媒介子和轻媒介子极限下推导了暗光子型媒介子的DM-电子散射截面的90%置信水平上限。对于$T=70^\boldsymbol{\rm \bullet C}$时最低阈值$E_{\rm th}=26.8\boldsymbol{\rm eV}$，该搜寻可探测低至$\boldsymbol{\rm \thicksim12 MeV}$的DM质量，其中接触相互作用的90%置信水平限在$m_\boldsymbol{\rm \thicksim100 MeV}$附近达到$2.7\times10^{-41}\boldsymbol{\rm cm^2}$，长程相互作用的90%置信水平限在$m_\boldsymbol{\rm \thicksim83 MeV}$附近达到$3.0\times10^{-37}\boldsymbol{\rm cm^2}$。因此，电子通道将InDEx的探测范围扩展至亚GeV DM质量，低至$\boldsymbol{\rm \thicksim O(10 MeV)}$，与其核反冲项目协同构成低质量暗物质的互补探测手段，提升了对主要与轻子耦合的DM候选者的灵敏度。
英文摘要
The Indian Dark Matter Search Experiment (InDEx) operates superheated droplet detectors with tetrafluoroethane ($\mathrm{C_2H_2F_4}$) as the active target at the Jaduguda Underground Science Laboratory (JUSL), and has so far probed dark matter (DM) through nuclear recoils at operating temperatures at which the target is insensitive to electron recoils. In this work, we consider six operating temperatures, $T=45$--$70\,^\circ\mathrm{C}$ in steps of $5\,^\circ\mathrm{C}$; the corresponding Seitz thresholds range from $0.61\,\mathrm{keV}$ down to $26.8\,\mathrm{eV}$. The ionization response of the $\mathrm{C_2H_2F_4}$ target is computed in the isolated-atom approximation from Roothaan--Hartree--Fock wavefunctions. The projected $90\%$ confidence-level upper limits on the DM--electron scattering cross section are derived for a dark-photon-type mediator in both the heavy- and light-mediator limits, for a benchmark exposure of $10^3\,\mathrm{kg\,days}$ under the zero-background assumption. For the lowest threshold, $E_{\rm th}=26.8\,\mathrm{eV}$ at $T=70\,^\circ\mathrm{C}$, the search probes DM masses down to $\sim 12\,\mathrm{MeV}$, with the $90\%$ confidence-level limit reaching $2.7\times10^{-41}\,\mathrm{cm}^2$ near $m_χ\simeq100\,\mathrm{MeV}$ for the contact interaction and $3.0\times10^{-37}\,\mathrm{cm}^2$ near $m_χ\simeq83\,\mathrm{MeV}$ for the long-range interaction. The electron channel thus extends the reach of InDEx to sub-GeV DM masses, down to $\mathcal{O}(10\,\mathrm{MeV})$, providing a complementary probe of low-mass dark matter alongside its nuclear-recoil program and enhancing sensitivity to DM candidates coupling predominantly to leptons.
Comments13 Pages, 8 Figures, 2 Tables
