Search for FCNC top quark processes at 7 TeV with the ATLAS detector

The first ATLAS results on the search for flavour changing neutral current~(FCNC) processes involving the top quark are presented. Data collected at a centre-of-mass energy $\sqrt{s}=7$~TeV during 2010 and corresponding to an integrated luminosity of 35~pb$^{-1}$ are used. The $t\to qZ$ decay channel is 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 leptonic decays of the $Z$ and $W$ bosons were considered ($Z\to e^+e^-,\mu^+\mu^-$ and $W\to e\bar\nu,\mu\bar\nu$) as signal. A search for anomalous single top quark production, through the FCNC direct process $qg\to t\to bW$, is also performed. No evidence for any FCNC signal is found. The upper limit on the $t\to qZ$ FCNC top quark decay branching ratio is $BR(t\to qZ)<17$\% at 95\% confidence level~(CL). For the single top quark production through FCNC, the observed 95\% CL cross-section times branching fraction limit is $\sigma_{qg\to t}\times$BR$(t\to bW)<17.3$~pb.