The DarkLight experiment has been proposed to search for a heavy photon, A'
in the mass range of 10-100 MeV/c$^2$ produced in electron-proton
collisions. Phase-I of DarkLight has started to take place in 2016 at the
Low Energy Recirculator Facility (LERF) at Jefferson Lab. LERF delivered a
100 MeV electron beam onto a windowless hydrogen gas target. The phase-I
detector tracks leptons inside the DarkLight solenoid with a set of Gas
Electron Multiplier (GEM) detectors, combined with segmented scintillators
for triggering. The GEM telescope consists of four
10x10 cm$^2$ triple layer GEM chambers with 2D readout strips, mounted in a
slightly angled fixed frame about 12 cm tall. The GEM data are read out with
analog pipeline front-end cards (APV-25) each of which can process 128
readout channels. Each GEM chamber has 250 channels for each coordinate
axis, read out with two APVs on each side, resulting in 2000 readout
channels for the GEM stack, processed by 16 APVs. One Multi Purpose
Digitizer (MPD) module is used to read out all of the 16 APV-25 cards. The
current run status of DarkLight experiment and the performance of GEMs in
the experiment will be discussed.
This work is presently supported by NSF PHY-1436680 and PHY-1505934.