Tracking performances of the dimuon spectrometer with a dipole magnet

The tracking performances of the ALICE forward muon spectrometer, with a dipole magnet, are investigated in this note. The study concerns the track finding and the mass resolution as well as the acceptance of the spectrometer for the Fi's, J/Psi and Gamma's. With the proposed setup, a mass resolution below 100 MeV is obtained and a track finding efficiency better than 90% is achieved for the heavy resonance. A absolute acceptance of 4.83 % is found which is acceptable in order to reach the requiered statistic for Gamma's' and Gamma's'' in Pb-Pb collisions.