Impact of a 10% increase of the Magnetic Field on the ATLAS Muon Spectrometer Performances

The excellent results obtained with the B0 prototype coil suggest that the final ATLAS toroidal magnet system may be operated at a current 10% higher than originally proposed. This note provides an evaluation of what would be the impact of the corresponding magnetic field upgrade on the physics performances of the Muon Spectrometer. It is shown that the gains in performances are such that it would allow to recover or even exceed the losses implied by the successive downscopings made to the magnet and detector systems.