Direct observation of avalanche scintillations in a THGEM-based two-phase Ar avalanche detector using Geiger-mode APD

TL;DR

This paper demonstrates the detection of avalanche scintillations in a two-phase argon detector using Geiger-mode APDs, showing potential for rare-event experiments with high sensitivity to near-infrared light.

Contribution

It introduces a novel optical signal recording method in two-phase avalanche detectors using G-APDs without wavelength shifters, and measures scintillation yields in a THGEM-based argon detector.

Findings

Detected 640 photoelectrons per 60 keV X-ray in argon at gain 400

Measured scintillation yield of 0.7 photoelectrons per avalanche electron

G-APD sensitivity extends to near-infrared scintillation light

Abstract

A novel concept of optical signal recording in two-phase avalanche detectors, with Geiger-mode Avalanche Photodiodes (G-APD) is described. Avalanche-scintillation photons were measured in a thick Gas Electron Multiplier (THGEM) in view of potential applications in rare-event experiments. The effective detection of avalanche scintillations in THGEM holes has been demonstrated in two-phase Ar with a bare G-APD without wavelength shifter, i.e. insensitive to VUV emission of Ar. At gas-avalanche gain of 400 and under \pm 70^\circ viewing-angle, the G-APD yielded 640 photoelectrons (pe) per 60 keV X-ray converted in liquid Ar; this corresponds to 0.7 pe per initial (prior to multiplication) electron. The avalanche-scintillation light yield measured by the G-APD was about 0.7 pe per avalanche electron, extrapolated to 4pi acceptance. The avalanche scintillations observed occurred presumably in the near infrared (NIR) where G-APDs may have high sensitivity. The measured scintillation yield is similar to that observed by others in the VUV. Other related topics discussed in this work are the G-APD's single-pixel and quenching resistor characteristics at cryogenic temperatures.