GEM Detectors for DarkLight Phase 1C

The DarkLight experiment has been proposed to search for a heavy photon A′ in the mass range of 10-100 MeV/c² produced in electron scattering. Inspired by the recent discovery (Krasznahorkay, A. J. et al., 2016) of an anomaly in the emission of di-leptons from excited Be⁸, interpreted as evidence for a fifth force carrier with a mass of 17 MeV/c², DarkLight Phase 1C will be focused on a dedicated search for a force carrier in the invariant mass region around 17 MeV/c².

The experiment aims to measure the process e^-Z → (e^-Z) e^-e⁺ with a Tantalum target, by detecting a charged lepton pair in the final state. If the lepton pair originates from the decay of a hypothetical neutral force particle, a peak structure in the invariant mass spectrum is expected. For Phase 1C a setup of two magnetic spectrometers is favored to detect the lepton pair with an invariant mass near 17 MeV/c². The spectrometers will be instrumented with customized GEM detectors for tracking. A novel GEM construction technique is used where all layers are stretched and assembled mechanically within a double frame.

 The preparation of GEM detector construction for the DarkLight Phase 1C experiment will be discussed.