Some Alignment Concepts for the GEM Muon Array

This report introduces a basic alignment scheme for the GEM muon detector. Optical straightness monitors are described, and their application discussed. Alternative alignment technologies are suggested and techniques are identified that can provide multipoint measurements. The problem of global alignment is posed, and several concepts are presented to attain the required precision. Some Alignment Concepts for the GEM Muon Array -J. Paradiso, June '92 Each phi sector of the muon detector array (i.e. "hexant") will be instrumented to monitor the relative alignment of its composite drift chamber layers. The most critical such measurement is the deviation in chamber alignment from a straight line along a muon path. If the 3 superlayers are relatively displaced along the muon bending direction, a false sagitta will result, leading to errors in the momentum measurement. In order to retain the quoted 5-10% momentum resolution of the GEM muon detector, the allowed misalignment of sense wires between chamber superlayers must be limited to ±25 μm (in the bending coordinate). Quad Photodiode Lens