A search for Flavour Changing Neutral Currents in Top Quark Decays t-> qZ at sqrt{s}=7 TeV in 0.70 fb$^{-1}$ of pp collision data collected with the ATLAS Detector

A search by the ATLAS collaboration for flavour changing neutral current~(FCNC) processes involving the top quark is presented. Data collected at a centre-of-mass energy of $\sqrt{s}=7$~TeV during 2011 corresponding to an integrated luminosity of 0.70~fb$^{-1}$ were used. Events in which one top quark decays via FCNC were searched for by looking for top quark pair production with one top quark decaying through FCNC ($t\to qZ$) and the other through the Standard Model dominant mode ($t\to bW$). Only the decays of the $Z$ boson to charged leptons and leptonic $W$ boson decays were considered as signal, leading to a final state topology characterised by the presence of three isolated leptons, at least two jets and missing transverse energy from the undetected neutrino. No evidence for an FCNC signal was found. An upper limit on the $t\to qZ$ branching ratio of BR$(t\to qZ)<1.1$\% is set at the 95\% confidence level, compatible with the expected limit, assuming no FCNC decay, of BR$(t\to qZ)<1.3\%$.