PandaX uses the two-phase xenon technique to build the dark matter detector. The materials used in the detector and shield are selected and screened for very low intrinsic radioactivity. The position resolution of the detector allows the definition of a fiducial volume that is well shielded from external sources of background. The primary scintillation light in the liquid phase, and the ionization signal via the electroluminescence in the gas phase will be combined to achieve a 1,000:1 rejection of gamma-ray backgrounds.

The principle of a two-phase Xe detector
The principle of a two-phase Xe detector

Advantages over the previous experiments include:

  • less background due to the very deep site;
  • the higher drift field in the TPC enhances the separation of gamma and neutron background events;
  • the disk-like geometry of the stage-1a detector enhances the light collection efficiency, thus lowering the energy threshold;
  • the vessels are made of very pure materials and the total mass of detector materials is reduced.