Limits on the luminance of dark matter from xenon recoil data

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^3–10, 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 squared (GeV/c ²), 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/c ².