UC Santa Cruz

A search for the flavour-changing neutral-current decay t→qZ$$t\rightarrow qZ$$ is presented. Data collected by the ATLAS detector during 2012 from proton–proton collisions at the Large Hadron Collider at a centre-of-mass energy of s=8$$\sqrt{s}=8$$ TeV, corresponding to an integrated luminosity of 20.3 fb-1$$^{-1}$$, are analysed. Top-quark pair-production events with one top quark decaying through the t→qZ$$t\rightarrow qZ$$ (q=u,c$$q=u,c$$) channel and the other through the dominant Standard Model mode t→bW$$t\rightarrow bW$$ are considered as signal. Only the decays of the Z boson to charged leptons and leptonic W boson decays are used. No evidence for a signal is found and an observed (expected) upper limit on the t→qZ$$t\rightarrow qZ$$ branching ratio of 7×10-4$$7\times 10^{-4}$$ (8×10-4$$8\times 10^{-4}$$) is set at the 95 % confidence level