Development of a Segmented GEM Readout detector

Abstract

Micromegas (Micro-MEsh GAseous Structures) detectors are a type of micro-pattern gaseous detectors. The primary charges are amplified in electron avalanches between a planar anode and a mesh typically 120 μm above the anode. For resistive anode type Micromegas detectors the signal is read out via copper readout strip layers below the anode. A 2D particle position can be reconstructed using two perpendicular readout strip layers below the resistive anode structure.Using a standard 2D resistive anode Micromegas readout structure, a unique 2D particle position reconstruction is only possible if the detector is hit by only one particle at the same time. Ambiguities will occur if multiple particles arrive at the same time. A unique X–Y assignment is strongly complicated.This issue can be resolved by replacing the mesh with a GEM (Gas Electron Multiplier) foil, which is segmented into 0.5 mm wide strips on at least one of the two sides. The GEM strips need to be turned by 45∘ with respect to the Micromegas readout strips. Thus the detector with a GEM foil segmented on both sides has four readout strip directions (X, Y, U and V) and a detector with a GEM foil segmented on only one side has three readout strip directions (X, Y and V).A prototype of such a Segmented GEM Readout (SGR) detector is built with GEM strips and readout strips perpendicular to each other. Test beam measurements with this detector were performed using 120 GeV muons. Results of the test beam measurements are presented here.