Event reconstruction in a liquid xenon Time Projection Chamber with an optically-open field cage

nEXO is a proposed tonne-scale neutrinoless double beta decay (0 nu beta beta) experiment using liquid Xe-136 (LXe) in a Time Projection Chamber (TPC) to read out ionization and scintillation signals. Between the field cage and the LXe vessel, a layer of LXe (``skin'' LXe) is present, where no ionization signal is collected. Only scintillation photons are detected, owing to the lack of optical barrier around the field cage. In this work, we show that the light originating in the skin LXe region can be used to improve background discrimination by 5% over previous published estimates. This improvement comes from two elements. First, a fraction of the gamma-ray background is removed by identifying light from interactions with an energy deposition in the skin LXe. Second, background from Rn-222 dissolved in the skin LXe can be efficiently rejected by tagging the.. decay in the Bi-214-Po-214 chain in the skin LXe.

Automated summary

The nEXO experiment proposes the use of light originating in the skin LXe region to improve background discrimination by 5%. This improvement comes from removing a fraction of gamma-ray background and efficiently rejecting background from Rn-222 dissolved in the skin LXe by tagging the decay in the Bi-214-Po-214 chain in the skin LXe.