Muon performance and related ATLAS fi rst physics

Muon final states provide clean signatures for many physics processes at LHC. Therefore, an excellent identification of muons and momentum resolution in a very wide energy is required. The performance of the ATLAS muon reconstruction and identification is here studied with the cosmic rays data recorded during the commissioning period and the first LHC proton-proton collision data at $sqrt{s}$= 7 TeV. Measured resolutions, efficiencies, muon isolation and residual distributions of reconstructed muon tracks are well reproduced by the Monte-Carlo simulation. In addition, the first observation in the ATLAS experiment of W and Z bosons in the muon channel at $sqrt{s}$= 7 TeV collisions is described. The selection yields to 40 $W o mu u$ and 2 $Z o mu mu$ candidates in a total integrated luminosity of approximately of 6.4 $nb^{-1}$ and 7.9 $nb^{-1}$ respectively, in agreement with Monte-Carlo expectations.