Prospects of charge signal analyses in liquid xenon TPCs with proportional scintillation in the liquid phase

TL;DR

This paper explores a single-phase liquid xenon TPC design utilizing proportional scintillation for improved charge signal analysis, offering enhanced resolution and background discrimination for dark matter detection.

Contribution

It introduces a novel single-phase detector concept with discrete electron counting and precise timing, improving energy resolution and background rejection over traditional dual-phase TPCs.

Findings

Enhanced low-energy signal resolution due to discrete electron counting.

Significant reduction in uncertainties from scintillation and detection processes.

Achieved 93% rejection efficiency in single vs. multiple site interaction discrimination.

Abstract

As liquid xenon TPCs increase in target mass while pursuing the direct detection of WIMP dark matter, the technical challenges arising due to their size call for new solutions and open the discussion on alternative detector concepts. Proportional scintillation in liquid xenon allows for a single-phase design evading all problems related to the liquid-gas interface and the precise gas gap required in a dual-phase TPC. Aside from a different scintillation mechanism, the successful detection- and analysis scheme of state-of-the-art experiments is maintained in this approach. We study the impact on charge signal analysis in a single-phase detector of DARWIN dimensions, where the fast timing of the proportional scintillation signal allows for the precise identification of the single electrons in the ionisation signal. Such a discrete electron-counting approach leads to a better signal resolution for low energies when compared to the classical dual-phase continuous method. The absence of the liquid-gas interface further benefits the S2-only energy resolution significantly. This reduces the uncertainties from the scintillation and signal-detection process to a level significantly below the irreducible fluctuation in the primary ionisation. Exploiting the precise electron time information further allows for a powerful single vs.~multiple site interaction discrimination with 93% rejection efficiency and 98% signal acceptance. This outperforms the design goal of the DARWIN observatory by a reduction factor of 4.2 in non-rejected multiple site neutron events.