Measurement of the Z to ll production cross section in proton-proton collisions at sqrt{s}=7 TeV with the ATLAS detector

This note describes the first measurement of the Z$\to\ell\ell$ production cross section, where $\ell$ = e, μ, by the ATLAS experiment. These results are based on 125 Z$\to\ell\ell$ candidates, produced in $\sqrt{s}=$7 TeV proton-proton collisions at the LHC and correspond to a total integrated luminosity of approximately 225 nb−1. The total inclusive Z-boson production cross section times the charged leptonic branching ratio within the invariant mass window 66 < mee < 116 GeV was measured to be [0.72±0.11(stat)±0.10(syst)±0.08(lumi)] nb for the Z $\to$ ee channel and [0.89 ± 0.10(stat) ± 0.07(syst) ± 0.10(lumi)] nb for the Z $\to$ μμ channel, resulting in a combined value of [0.83 ± 0.07(stat) ± 0.06(syst) ± 0.09(lumi)] nb. This constitutes the first Z cross-section measurement by ATLAS in proton-proton collisions at $\sqrt{s}=$7 TeV and the results obtained are in agreement with theoretical calculations based on NNLO QCD.