Event Reconstruction in a Liquid Xenon Time Projection Chamber with an Optically-Open Field Cage

TL;DR

This paper demonstrates that detecting scintillation light from the skin LXe region in a liquid xenon TPC can enhance background discrimination by identifying gamma interactions and radon decay events, improving the sensitivity of neutrinoless double beta decay searches.

Contribution

It introduces a novel method of using scintillation light from the skin LXe to improve background rejection in a liquid xenon TPC for $0 uetaeta$ experiments.

Findings

Background discrimination improved by 5% using skin LXe scintillation signals.

Gamma-ray background can be reduced by identifying interactions in the skin LXe.

Radon-related background can be efficiently tagged via alpha decay detection.

Abstract

nEXO is a proposed tonne-scale neutrinoless double beta decay ($0\nu\beta\beta$) experiment using liquid ${}^{136}Xe$ (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 ${}^{222}Rn$ dissolved in the skin LXe can be efficiently rejected by tagging the $\alpha$ decay in the ${}^{214}Bi-{}^{214}Po$ chain in the skin LXe.