It is commonly conjectured that dark matter is a charge neutral fundamental particle. However, it may still have minute photon-mediated interactions through millicharge^1,2 or higher-order multipole interactions^{3,4,5,6,7,8,9,10}, resulting from new physics at a high energy scale. Here we report a direct search for effective electromagnetic interactions between dark matter and xenon nuclei that produce a recoil of the latter from the PandaX-4T xenon-based detector^11,12. Using this technique, the first constraint on the charge radius of dark matter is derived with the lowest excluded value of 1.9 × 10⁻¹⁰ fm² for a dark matter mass of 40 giga electron volts per speed of light in a vaccum (GeV/c²) more stringent than that for neutrinos by four orders of magnitude. Constraints on the magnitudes of millicharge, magnetic dipole moment, electric dipole moment and anapole moment are also improved substantially from previous searches^13,14, with corresponding tightest upper limits of 2.6 × 10⁻¹¹ e, 4.8 × 10⁻¹⁰ Bohr magnetons, 1.2 × 10⁻²³ ecm and 1.6 × 10⁻³³ cm², respectively, for a dark matter mass of 20–40 GeV/c².

通常推测暗物质是一种电荷中性的基本粒子。然而，它可能仍然有微小的光子介导的相互作用，通过毫电荷^1,2或更高阶的多极相互作用^{3,4,5,6,7,8,9,10}，这是高能尺度的新物理学产生的。在这里，我们报告直接搜索暗物质和氙原子核之间的有效电磁相互作用，这些相互作用从 PandaX-4T 基于氙的探测器^11,12产生后者的反冲。使用这种技术，对于真空中每光速 40 吉电子伏特的暗物质质量^{( GeV}  / c² ) 比中微子严格四个数量级。与之前的搜索相比，毫电荷、磁偶极矩、电偶极矩和反极矩的大小限制也得到了显着改善^13,14，相应的最严格上限为 2.6 × 10 ^-11  e、4.8 × 10 ^-10 玻尔磁子、1.2 × 10 ^-23  ecm 和 1.6 × 10 ^-33  cm ²，暗物质质量为 20–40 GeV/ c ²。