Search for $t\bar{t}Z$ production in the three lepton final state with $4.7$ ${\rm fb}^{-1}$ of $\sqrt{s}=7$ TeV $pp$ collision data collected by the ATLAS detector

A search for $t\bar{t}Z$ production with the ATLAS detector in $pp$ collisions at the LHC is presented. The search is performed on $4.7$ ${\rm fb}^{-1}$ of data collected in 2011. Only final states with three leptons are considered, in which the $Z$ boson decays to a pair of leptons and one of the $W$ bosons coming from $t\to bW$ decays gives rise to a lepton after decay. One candidate event passing the selection cuts is observed in data with an expected background of $0.28^{+1.57}_{-0.14}$ events. A 95% credibility upper limit of $0.71$ pb on the cross section of ${t\bar{t}Z}$ production is set using a Bayesian prescription, consistent with the Standard Model prediction of 0.14 pb.