In-Situ Determination of the Performance of the Muon Spectrometer

The ATLAS muon spectrometer consists of three layers of precision drift-tube chambers in a toroidal magnetic with a field integral between 2.5 and 6 Tm. Muon tracks are reconstructed with 97% efficiency and a momentum resolution between 3% and 4% for 10 GeV< pT <500 GeV and better than 10% for transverse momenta up to 1 TeV. In this note, the performance of a perfectly calibrated and aligned muon spectrometer will be reviewed and the impact of deteriorations of the magnetic field, the calibration and misalignment of the muon chambers on the performance will be discussed. The main part of the note describes how the performance of the muon spectrometer can be determined using dimuon decays of Z bosons and J /ψ mesons.