Abstract : The LHC is a proton collider located at CERN with 14 TeV in the center-of-mass. The first collisions are expected at the end of 2009. The ATLAS experiment is one of the two general-purpose LHC experiments. The available energy and its high luminosity will allow the ATLAS experiment to search for the Higgs boson along with other new particles predicted by physics models beyond the standard model. Muons are of major importance for the measurement of the standard model and the search for new physics. They also provide valuable insight on the performance of the detector. In this thesis, the direct search of Z' decaying into two muons has been studied. A small number of events is enough for discovering a Z' and is possible with the first data. We shall study in particular the effects of the muon spectrometer alignment on high pT tracks and on the Z' discovery potential in the ATLAS experiment. At start up of the LHC, the muon spectrometer alignment will not have reached the nominal performances. High pT muons have been used to estimate the impact of a degraded alignment on track reconstruction. Results are given in terms of reconstruction efficiency, momentum and invariant mass resolution, charge identification and the sensibility for the discovery or for the exclusion. For the first LHC data an analysis with the muon spectrometer only is necessary. Finally, a complete study to determine the initial geometry of the muon spectrometer using tracks without toroidal magnetic field has been done including an estimate of the beam time necessary to achieve a given alignment accuracy.