Measurement of the W->lnu production cross-section and observation of Z -> ll production in proton-proton collisions at root{s}=7 TeV with the ATLAS detector

This note describes the first measurement of the W->lnu production cross section and an observation of Z->ll production, where l = e,μ, by the ATLAS experiment. These results are based on 118 W->lnu candidates and 14 Z->ll candidates, produced in sqrt(s) = 7 TeV proton-proton collisions at the LHC and correspond to a total integrated luminosity of approximately 17 nb−1. The total inclusive W-boson production cross section times the leptonic branching ratio is measured to be (8.5 ± 1.3(stat) ± 0.7(syst) ± 0.9(lumi)) nb for the W->enu channel and (10.3 ± 1.3(stat) ± 0.8(syst) ± 1.1(lumi)) nb for the W->μnu channel. This constitutes the first W cross-section measurement by ATLAS in proton-proton collisions and the result obtained is in agreement with theoretical calculations based on NNLO QCD. In addition the expected charge asymmetry between the cross sections for W+ and W− production is experimentally confirmed.