Reducing the background levels of GEM detectors in high rate environments of SBS experiments at JLab*

The Gas Electron Multiplier (GEM) detectors built at UVa are used for both front and rear tracking systems for SBS experiments at JLab. These detectors meet all critical requirements of the SBS program, including being able to handle rates as high as 500 kHz/cm2, and providing an excellent spatial resolution of 70 µm. However, a higher than predicted background levels that resulted from the intense low energy photon environment in the SBS experiments led to reduced efficiency and increased difficulty in GEM detector tracking. Our research focuses on reducing the background hits created in the GEM detector due to radiation interaction with the chamber components. To achieve this, a Geant4 simulation of a 10cm x 10cm GEM module has been developed to optimize the configuration of the cathode foil and the top GEM foil by varying their material and thickness to lower the effects of high background rates. Different prototype 10cm x 10cm GEM modules are constructed with various configurations of cathode foils and top GEM foils. Data is taken while the prototypes are exposed to an X-ray beam in the detector lab at UVa to validate the simulated results. Simulation results for the different configurations compared to experimental data will be presented.

US Department of Energy, Office of Science, Office of Nuclear Physics award number DE-FG02-03ER41240