Development and Performance of a Sealed Liquid Xenon Time Projection Chamber.

The liquid xenon (LXe) time projection chamber (TPC) technology is probing a wide range of dark matter masses from sub-GeV to a few TeV. To further improve its sensitivity to sub-GeV dark matter and its application in reactor neutrino monitoring via coherent elastic neutrino-nucleus scattering (CEvNS), more understanding and suppression of single/few electrons background rate are needed. Here we report on the design and performance of a sealed LXeTPC with a graphene-coated fused silica window as the cathode. The purpose of the sealed TPC is for isolating the liquid xenon target volume from the majority of out-gassing materials in the detector vessel, thus improving the liquid xenon purification efficiency and reducing the impurity-induced single/few electrons background. We investigated the out-gassing rate and purification efficiency using the data from the sealed TPC with a simple purification model. The single electron signals from the photoionization of impurities in LXe are obtained and their correlation with the LXe purity is investigated. The photo-electron emission rate on the graphene-coated electrode is compared to that from stainless steel, the electrode material typically used in LXe detectors. We discuss the possible further improvement and potential applications of the sealed TPC for the next generation liquid xenon experiments for dark matter and neutrino physics.