Measurement of the W → ℓν and Z/γ * → ℓℓ production cross sections in proton-proton collisions at s = 7\;TeV with the ATLAS detector

First measurements of the W and Z/ * ( = e, ) production cross sections in proton-proton collisions at s = 7 TeV are presented using data recorded by the ATLAS experiment at the LHC. The results are based on 2250 W and 179 Z/ * candidate events selected from a data set corresponding to an integrated luminosity of approximately 320 nb -1 . The measured total W and Z/ * -boson production cross sections times the respective leptonic branching ratios for the combined electron and muon channels are tot W BR(W ) = 9.96 0.23(stat) 0.50(syst) 1.10(lumi) nb and tot Z/ * BR(Z/ * ) = 0.82 0.06 (stat) 0.05 (syst) 0.09 (lumi) nb (within the invariant mass window 66 < m < 116 GeV). The W/Z cross-section ratio is measured to be 11.7 0.9(stat) 0.4(syst). In addition, measurements of the W + and W -production cross sections and of the lepton charge asymmetry are reported. Theoretical predictions based on NNLO QCD calculations are found to agree with the measurements.