Single electron multiplication distribution in GEM avalanches

TL;DR

This study measures the electron multiplication distribution in GEM detectors, revealing how different gases affect the avalanche response and intrinsic resolution, with implications for detector performance optimization.

Contribution

It provides detailed experimental measurements of single-electron avalanche distributions in GEMs and analyzes the influence of working gases on these distributions and detector resolution.

Findings

Distribution has an exponential tail at large amplitudes.

Gas type influences the shape of the multiplication distribution.

Neon-based mixture achieves a sigma-over-mean ratio of 0.75.

Abstract

In this paper, measurement results and experimental methodology are presented on the determination of multiplication distributions of avalanches initiated by single electron in GEM foils. The measurement relies on the amplification of photoelectrons by the GEM under study, which is subsequently amplified in an MWPC for signal enhancement and readout. The intrinsic detector resolution, namely the sigma-over-mean ratio of the multiplication. distribution is also elaborated. Small gain dependence of the shape of the avalanche response distribution is observed in the range of net effective gain of 15 to 100. The distribution has an exponentially decaying tail at large amplitudes. At small amplitudes, the applied working gas is seen to have a well visible effect on the shape of the multiplication distribution. Equivalently, the working gas has an influence on the intrinsic detector resolution of GEMs via suppression of the low amplitude responses. A sigma-over-mean ratio of 0.75 was reached using a neon based mixture, whereas other gases provided an intrinsic detector resolution closer to 1, meaning a multiplication distribution closer to the low-field limit exponential case.