Study of GEM Foil Etching Techniques on Detector Performance

The LHC will undergo a major upgrade, named the High-Luminosity LHC (HL-LHC), that will deliver instantaneous luminosity as high as 7×10³⁴ cm^-2 s^-1. To cope with the higher event rates and with the increased radiation doses, the Compact Muon Solenoid (CMS) experiment will undergo several upgrades including the installation of additional muon detectors based on the Gas Electron Multiplier (GEM) technology.GEM foils, the core of GEM-based detectors, are currently produced with either double-mask or single-mask etching. Single-mask etching is a promising method, but results in an asymmetry in the shape of the holes. The effect of the hole asymmetry on the detector performance was studied with a twofold approach. Experimental data were collected using GEM foils with different hole geometries and detailed simulations were performed matching the experimental conditions. We present an overview of GEM detectors in CMS and describe a study to assess the impact of the GEM hole asymmetry on the detector performance.