Recent Advances in Bubble-Assisted Liquid Hole Multipliers in Liquid Xenon

TL;DR

This paper reports recent progress in bubble-assisted Liquid Hole Multipliers in liquid xenon, demonstrating high electroluminescence yields, improved configurations, and new operational modes for enhanced particle detection.

Contribution

It introduces novel electrode configurations and operational modes for LHMs, achieving higher EL yields and demonstrating two-stage and vertical-mode operations in liquid xenon.

Findings

125 μm-thick SC-GEM achieved highest EL yield (~400 photons/electron)

EL yield increased fivefold with high transfer fields

First demonstration of two-stage and vertical-mode LHM operation

Abstract

We report on recent advances in the operation of bubble-assisted Liquid Hole Multipliers (LHM). By confining a vapor bubble under or adjacent to a perforated electrode immersed in liquid xenon, we could record both radiation-induced ionization electrons and primary scintillation photons in the noble liquid. Four types of LHM electrodes were investigated: a THGEM, standard double-conical GEM, 50 $\mu$m-thick single-conical GEM (SC-GEM) and 125 $\mu$m-thick SC-GEM - all coated with CsI photocathodes. The 125 $\mu$m-thick SC-GEM provided the highest electroluminescence (EL) yields, up to ~400 photons per electron over 4$\pi$ with an RMS pulse-height resolution reaching 5.5% for events comprising ~7000 primary electrons. Applying a high transfer field across the bubble, the EL yield was further increased by a factor of ~5. The feasibility of a vertical-mode LHM, with the bubble confined between two vertical electrodes, and the operation of a two-stage LHM configuration were demonstrated for the first time. We combine electrostatic simulations with observed signals to draw conclusions regarding the location of the liquid-gas interface and suggest an explanation for the observed differences in EL yield between the investigated electrodes.