ATLAS collaboration (2879 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 AntonioPinto, BelmiroSantos, HelenaSaraiva, JoãoSilva, JoséTavares Delgado, AdemarVeloso, FilipeWolters, Helmut2019-02-042019-02-042015-02-18http://dx.doi.org/10.1140/epjc/s10052-014-3233-4http://hdl.handle.net/10400.26/26710A search for the production of single-top-quarks in association with missing energy is performed in proton–proton collisions at a centre-of-mass energy of $\sqrt{s}=\mathrm {8~TeV}$ with the ATLAS experiment at the large hadron collider using data collected in 2012, corresponding to an integrated luminosity of $20.3$  fb$^{-1}$ . In this search, the $W$ boson from the top quark is required to decay into an electron or a muon and a neutrino. No deviation from the standard model prediction is observed, and upper limits are set on the production cross-section for resonant and non-resonant production of an invisible exotic state in association with a right-handed top quark. In the case of resonant production, for a spin- $0$ resonance with a mass of $500$  GeV, an effective coupling strength above $0.15$ is excluded at 95 $\,\%$ confidence level for the top quark and an invisible spin- $1/2$ state with mass between $0$ and $100$  GeV. In the case of non-resonant production, an effective coupling strength above $0.2$ is excluded at 95 $\,\%$ confidence level for the top quark and an invisible spin- $1$ state with mass between $0$ and $657$  GeV.engjournal article2019-02-04