Search for Light Inelastic Dark Matter with Low-Energy Ionization Signatures in PandaX-4T

Direct detection of light dark matter (DM) is generally difficult due to its small recoil energy. The inelastic scattering of DM can produce unique signatures in the DM direct detection experiments. Using the low-energy unpaired ionization data from PandaX-4T, we newly analyze the probe of the exothermic inelastic dark matter (ineDM). We demonstrate that PandaX-4T can probe the ineDM mass-splitting down to 0.05 keV and probe the ineDM mass to the sub-GeV range. For the ineDM with a dark photon mediator, we use the PandaX-4T data to impose stringent bounds on the mixing parameter between the dark photon and photon.