W and Z Production in pp Collisions at 7 TeV with the ATLAS Experiment at the LHC

The observation of W and Z bosons and a measurement of the production cross sections in proton proton collisions at E_CM = 7 TeV are presented using data from the ATLAS experiment at the LHC. Results are based on 118 W -> lnu and 125 Z/gamma* -> ll (l=e,mu) candidate events corresponding to an integrated luminosity of about 17 nb^-1 and 225 nb^-1 respectively. The measured values of sigma_W x BR(W -> lnu) = 9.3 \pm 0.9 (stat) \pm 0.6 (syst) \pm 1.0 (lumi) nb and sigma_Z/gamma* x BR(Z/gamma* -> ll, 66<m_ll<116) = 0.83 \pm 0.07 (stat) \pm 0.06 (syst) \pm 0.09 (lumi) nb. A measurement of the W lepton charge asymmetry is also reported. A comparison with theoretical predictions based on NNLO QCD calculations shows agreement with the measurements.