ATLAS collaboration (2855 authors)Aguilar-Saavedra, Juan AntonioAmor Dos Santos, Susana PatriciaAnjos, NunoAraque, Juan PedroCantrill, RobertCarvalho, JoãoCastro, Nuno FilipeConde Muiño, PatriciaDa Cunha Sargedas De Sousa, Mario JoseFiolhais, MiguelGalhardo, BrunoGomes, AgostinhoGonçalo, RicardoJorge, PedroLopes, LourencoMachado Miguens, JoanaMaio, AméliaManeira, JoséOnofre, AntónioPalma, AlbertoPedro, RutePina, João AntonioSantos, HelenaSaraiva, JoãoSilva, JoséTavares Delgado, AdemarVeloso, FilipeWolters, Helmut2019-02-052019-02-052016-01-08http://dx.doi.org/10.1140/epjc/s10052-015-3851-5http://hdl.handle.net/10400.26/27743A search for the flavour-changing neutral-current decay $t\rightarrow qZ$ 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 $\sqrt{s}=8$  TeV, corresponding to an integrated luminosity of 20.3 fb$^{-1}$ , are analysed. Top-quark pair-production events with one top quark decaying through the $t\rightarrow qZ$ ( $q=u,c$ ) channel and the other through the dominant Standard Model mode $t\rightarrow bW$ 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 $t\rightarrow qZ$ branching ratio of $7\times 10^{-4}$ ( $8\times 10^{-4}$ ) is set at the 95 % confidence levelengjournal article2019-02-05