Performance of an MDT cosmic test stand: a Monte Carlo evaluation

The high level of mechanical accuracy in the wire location represents one of the main characteristics of the MDT chambers. The X-ray measurements performed at CERN have certified this accuracy; almost all the measured chambers have an r.m.s. respect to the nominal position below 20 mm. It has been also observed that, leaving free, in the fit to the measured wire grid, few global parameters, like the relative distance, the rotation and the angle between multilayers (chamber mechanical parameters), we can obtain a substantial improvement (up to 5-7 mm) in the wire r.m.s. that can boost the ultimate precision of the Atlas muon spectrometer. Only a small (10-15%) fraction of all MDTs can be X-ray inspected at the CERN Tomograph [2], but all the chambers are expected to be certified in a cosmic rays stand. We can therefore try to optimize the chamber geometrical parameters from the analysis of the cosmic rays data. The aim of this note is the Monte Carlo evaluation of the performance of a simple cosmic rays test facility, looking in particular to the resolution that can be obtained in the measurements of the chamber geometrical parameters.