Construction and Performance of a Large Area GEM detector with Low Mass and Zigzag-strip Readout*

We present the construction of a low-mass, low cost, large area GEM detector and its performance in a 120 GeV proton beam. This design is optimized for forward tracking in the future Electron Ion Collider (EIC) by reducing multiple scattering via decreased material budget. In the forward and backward regions, tracking resolution is critical for reconstruction and identification; but is diminished with multiple scattering through high Z materials. This design uses seven times less material than a standard Triple GEM (TGEM) installed in the CMS muon end-cap. To meet the low material budget, the drift and readout electrodes are manufactured on foils instead of PCBs. The drift, TGEM, and readout foils are enclosed in two trapezoidal carbon fiber frames with aluminized polyimide foil windows. The frames are cut from a contiguous carbon-fiber plate and include a support beam in the center, parallel to the base, to protect the drift from potential window sagging. To further protect the drift electrode, the aluminized inner side of the window is held at the same voltage to decrease the attractive coulomb force. This design shows comparable gas gain and HV stability to a common GEM. The readout strips were chosen to have a radial zigzag geometry to decrease the number of channels; hence the associated cost of manufacturing, while still maintaining optimal spatial resolution. This design was tested at FermiLab's Proton Test Beam facility and the data is currently being analyzed for its angular resolution as a function of sector and zigzag dimensions. At present, the average strip multiplicity of the straight strip section is 4 at an applied voltage of 4.4kV.