Proportional scintillation in liquid xenon: demonstration in a single-phase liquid-only time projection chamber

TL;DR

This paper demonstrates proportional scintillation detection in a single-phase liquid xenon TPC, showing it as a viable alternative to dual-phase detectors for dark matter searches with detailed characterization and measurement of key parameters.

Contribution

It introduces a novel single-phase liquid xenon TPC design that effectively detects proportional scintillation signals, expanding the options for dark matter detection technology.

Findings

Achieved a charge gain factor of up to 1.9 PE/electron.

Measured electron drift velocity and diffusion constants consistent with literature.

Successfully operated a single-phase TPC with proportional scintillation detection.

Abstract

The largest direct dark matter search experiments to date employ dual-phase time projection chambers (TPCs) with liquid noble gas targets. These detect both the primary photons generated by particle interactions in the liquid target, as well as proportional secondary scintillation light created by the ionization electrons in a strong electric field in the gas phase between the liquid-gas interface and the anode. In this work, we describe the detection of charge signals in a small-scale single-phase liquid-xenon-only TPC, that features the well-established TPC geometry with light readout above and below a cylindrical target. In the single-phase TPC, the proportional scintillation light (S2) is generated in liquid xenon in close proximity to 10 {\mu}m diameter anode wires. The detector was characterized and the proportional scintillation process was studied using the 32.1 keV and 9.4 keV signals from 83mKr decays. A charge gain factor g2 of up to (1.9 $\pm$ 0.3) PE/electron was reached at an anode voltage 4.4 kV higher than the gate electrode 5 mm below it, corresponding to (29 $\pm$ 6) photons emitted per ionization electron. The duration of S2 signals is dominated by electron diffusion and approaches the xenon de-excitation timescale for very short electron drift times. The electron drift velocity and the longitudinal diffusion constant were measured at a drift field of 470 V/cm. The results agree with the literature and demonstrate that a single-phase TPC can be operated successfully.