Direct observation of bubble-assisted electroluminescence in liquid xenon

TL;DR

This study directly observed bubble-assisted electroluminescence in liquid xenon, linking bubble formation to photon emission and demonstrating potential for improved noble-liquid TPCs.

Contribution

First direct observation of bubble-assisted electroluminescence in liquid xenon, confirming the mechanism and exploring controlled bubble formation for detector applications.

Findings

Bubbles correlate with electroluminescence signals.

Controlled bubble formation achieved energy resolution of ~7.5%.

Phenomenon suggests new design avenues for noble-liquid TPCs.

Abstract

Bubble formation in liquid xenon underneath a Thick Gaseous Electron Multiplier (THGEM) electrode immersed in liquid xenon was observed with a CCD camera. With voltage across the THGEM, the appearance of bubbles was correlated with that of electroluminescence signals induced by ionization electrons from alpha-particle tracks. This confirms recent indirect evidence that the observed photons are due to electroluminescence within a xenon vapor layer trapped under the electrode. The bubbles seem to emerge spontaneously due to heat flow from 300K into the liquid, or in a controlled manner, by locally boiling the liquid with resistive wires. Controlled bubble formation resulted in energy resolution of {\sigma}/E~7.5% for ~6,000 ionization electrons. The phenomenon could pave ways towards the conception of large-volume 'local dual-phase' noble-liquid TPCs.