Joseph A. Paradiso, Daniel R. Marlow

Abstract

In order to perform a precision measurement of high pt muon tracks, the mechanical alignment of the GEM muon drift chambers was to be monitored with extraordinary accuracy; i.e., the sagitta error induced into muon tracks by superlayer misalignments must be held within 25 microns RMS across spans of several meters. As there are thousands of chambers to monitor, the resulting system must be simple, reliable, and inexpensive. The GEM muon group has explored two types of alignment sensors for this application, namely three-point Video Straightness Monitors and stretched wires with mini-strip pickup pads and axial pickup rings. This paper gives an overview of these systems and describes their associated electronics.