GEM Detector Construction for DarkLight Phase 1C

DarkLight Phase 1C was proposed as a dedicated search to verify the proclaimed 17-MeV fifth-force carrier observed in the emission of di-leptons from excited Be. The setup is based on two magnetic spectrometers to detect the lepton pair, instrumented with customized large area GEM detectors for tracking.
A novel GEM construction technique is used where all layers are stretched and assembled mechanically within a double frame. The readout will be based on APVs and MPDs. The key features of these detectors allows them to be used very flexibly in high-rate environments for high-resolution charged particle tracking. The present status of the construction, design features and expected performance of the GEM detectors will be discussed.