Simulation study of ternary gas mixture transport properties and their gain in GEM detectors used for muon tracking

Gas electron multiplier (GEM) has been installed in the high η region of the Compact Muon Solenoid experiment (CMS) because as example of its high-rate capability. The operational gas of the GEM plays an important role in providing an efficient detection of muon. This work aims to search for a safe and a high-performance gas mixture through a numerical study of the transport properties of ternary gas mixtures. The gas mixtures consists of a noble gas (Ar-Ne-Xe-He) mixed with CO₂ and a third gas (N₂-C₅H₁₂ -CH₄ - iC₄H₁₀) with different proportions. The gain of single and triple GEM for the mixtures, which show optimal properties, is calculated to estimate their performance in the detector. It is found that the N₂ included mixture is giving a high drift velocity while the C₅H₁₂ based mixture has the highest Townsend coefficient, which results in higher gain in both single and triple GEM.