The PandaX-III project searches for the possible neutrinoless double-beta decay ($0\nu\beta\beta$) of ${}^{136}Xe$: ${}^{136}Xe \rightarrow {}^{136}Ba + 2e^-$ with 200 kg to one ton of 90% enriched ${}^{136}Xe$ as the source. The high-pressure gas Time Projection Chamber (TPC) we use can measure the energies of the two emitted electrons from $0\nu\beta\beta$ and image the electron tracks, and thus can effectively identify $0\nu\beta\beta$ signals and suppress the unwanted backgrounds.
Our TPC is symmetrical with the negative high voltage in the middle. Electrons ionized by an energy release in the TPC drift to either end, where Micromegas is used to amplify and collect the charges. The expected spatial resolution is 3 mm and the energy resolution is 3%.
At SJTU, we built 20 kg scale prototype detectors, consisting of a stainless steel pressure vessel and a single-end TPC. We optimized the design of the Micromegas readout plane, finalized the energy calibration of the TPC, and developed algorithms for 3D electron track reconstruction.