The $Z\to \tau \tau$ cross section is measured with the ATLAS experiment at the LHC in four different final states determined by the decay modes of the $\tau$ leptons: muon-hadron, electron-hadron, electron-muon, and muon-muon. The analysis is based on a data sample corresponding to an integrated luminosity of $36{\mathrm{pb}}^{-1}$, at a proton-proton center-of-mass energy of $\sqrt{s}=7\mathrm{TeV}$. Cross sections are measured separately for each final state in fiducial regions of high detector acceptance, as well as in the full phase space, over the mass region 66–116 GeV. The individual cross sections are combined and the product of the total $Z$ production cross section and $Z\to \tau \tau$ branching fraction is measured to be $0.97\pm 0.07(\mathrm{stat})\pm 0.06(\mathrm{syst})\pm 0.03(\mathrm{lumi})\mathrm{nb}$, in agreement with next-to-next-to-leading order calculations.

• Received 9 August 2011

DOI:https://doi.org/10.1103/PhysRevD.84.112006

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© 2011 CERN, for the ATLAS Collaboration