Hole misalignment and gain performance of Gaseous Electron Multipliers

It is well known and has been shown that the gain performance of Gaseous Electron Multipliers (GEM) depends on size holes. With an optical scanner it possible to measure dimensions holes, predict GEMs. However, prediction GEMs are manufactured with a double mask etching technique not straightforward. hole information alone, make precise gain. We show alignment photo-masks between two sides GEM foils plays crucial role. A misalignment few microns can lower substantially. The study performed by using Helsinki high definition for quality control foils, this will its true potential.