Development and Characterization of MPGD-based Transition Radiation Detectors

TL;DR

This work evaluates MPGD-based transition radiation detectors (TRDs) as scalable, high-rate alternatives to traditional wire-based amplification. By prototyping and beam-testing triple-GEM, Micromegas, and μRWELL TRDs with fleece and foil radiators, the study assesses gain stability, TR photon discrimination, and electron/pion separation in mixed beams at FTBF and CERN SPS. The GEM-based TRD demonstrates the strongest, most stable performance (pion suppression up to ~8 at 90% electron efficiency in some setups), while Micromegas benefits from a GEM preamplifier and shows improved TR sensitivity; μRWELL faces gain limitations under the tested conditions. Geant4 simulations corroborate the observed trends and emphasize the critical roles of cathode material and radiator configuration in shaping TR yield. Overall, the results confirm MPGD-based TRDs as viable foundations for next-generation electron identification in high-rate experiments and guide optimization of radiator, drift, and amplification design for enhanced performance.

Abstract

Transition Radiation Detectors (TRDs) are useful for electron identification and hadron suppression in high energy nuclear and particle physics experiments. Conventional wire-chamber TRDs face operational limitations due to space charge effects, motivating the replacement of the amplification stage with MicroPattern Gaseous Detectors (MPGDs). In this work, we explore different MPGD technologies - Gas Electron Multiplier (GEM), Micro-Mesh Gaseous Structure (Micromegas), and Resistive Micro-Well (microRWELL) - as alternative TRD amplification stages. We report on the design, construction, and in-beam characterization of three MPGD-based TRD prototypes exposed to 3-20 GeV mixed electron-hadron beams at the Fermilab Test Beam Facility (FTBF) and at the CERN SPS H8 beamline. Each detector consisted of a multi-layered radiator, an approximately 2 cm deep drift region, an MPGD amplification stage optimized for X-ray transition radiation detection in a 90%10% ratio of Xenon and CO2, and a two-dimensional readout. The GEM-based TRD prototype achieved a pion suppression factor of about 8 at 90% electron efficiency at FTBF, while the Micromegas-based prototype - with an added GEM preamplification layer - demonstrated improved gain stability and clear TR photon discrimination at CERN. The microRWELL prototype achieved stable operation but limited gain. Geant4-based studies confirmed the observed trends and highlighted the sensitivity of the TR yield to cathode material and radiator configuration. These studies represent the first in-beam measurements of Micromegas- and microRWELL-based TRDs, along with discussion of the performance capabilities of a triple-GEM-TRD. The results demonstrate the feasibility of MPGDs as scalable, high-rate amplification structures for next-generation TRD applications.

Figures (13)

• Figure 1: (Top) Cross-sectional schematic of the GEM-TRD_v1 design, as tested at FTBF; (Bottom) cross-sectional schematic of the GEM-TRD_v2 design, as tested at CERN SPS. Note the schematics are not to scale.
• Figure 2: (Top) Cross-sectional schematic of the Micromegas-TRD prototype, as tested at FTBF; (Bottom) cross-sectional schematic of the Micromegas+GEM-TRD, as tested at CERN SPS. Note the schematics are not to scale.
• Figure 3: (Top) Picture of the fully assembled $\upmu$RWELL-TRD from above; (Bottom) cross-sectional schematic of the $\upmu$RWELL-TRD prototype.
• Figure 4: Example of a typical raw fADC-125 waveform for the GEM-TRD_v2 (Top) and the Micromegas+GEM-TRD (Bottom).
• Figure 5: (Top) Experimental setup used for the FTBF test beam measurements. Note that the Fermilab-owned Cherenkov detectors are not pictured, since they are upstream from the setup. (Bottom) Schematic of the detector layout for the FTBF test beam experimental setup (not to scale). The various components are described in the document text.