Alignment of the ATLAS muon spectrometer with Muon Tracks

Abstract

The ATLAS muon spectrometer uses three layers of precision drift-tube chambers to measure muon momenta accurately up to the TeV scale in an air-core toroid magnet system providing a field integral of 2.5 to 7 Tm. In order to achieve the required momentum resolution of better than 4% for transverse momenta below 400 GeV/c and of 10% at 1 TeV/c, the relative positions of the muon chambers must be known with 30 μm accuracy. A system of optical alignment sensors monitors relative movements of the chambers with a few micrometers accuracy. It is capable of measuring the relative chamber positions with an accuracy better than 30 μm after it has been calibrated with straight tracks. These will be provided by special runs with the magnets turned off. We present results of Monte-Carlo studies for the alignment with straight tracks recorded with proton-proton collisions at the LHC and cosmic muon data.