Preparation of GEM detectors for DarkLight

The DarkLight experiment will search for a dark photon in the 10-20 MeV/c² mass region and examine the reported evidence for the X17 boson using electroproduction of electron-positron pairs from a tantalum target. The first stage of the experiment has been approved and is under preparation at the ARIEL electron accelerator at TRIUMF. The experimental setup consists of two high-resolution magnetic spectrometers, with the focal planes instrumented identically with two layers of high spatial-resolution Gas Electron Multipliers (GEM) and trigger scintillator hodoscope arrays, suitable to operate with high efficiency under high-intensity condition. Details of the GEM detector preparation and commissioning will be reported.