Search for invisible particles produced in association with single-top-quarks in proton-proton collisions at...

A 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 [Formula: see text] with the ATLAS experiment at the large hadron collider using data collected in 2012, corresponding to an integrated luminosity of [Formula: see text] fb[Formula: see text]. In this search, the [Formula: see text] 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-[Formula: see text] resonance with a mass of [Formula: see text] GeV, an effective coupling strength above [Formula: see text] is excluded at 95[Formula: see text] confidence level for the top quark and an invisible spin-[Formula: see text] state with mass between [Formula: see text] and [Formula: see text] GeV. In the case of non-resonant production, an effective coupling strength above [Formula: see text] is excluded at 95[Formula: see text] confidence level for the top quark and an invisible spin-[Formula: see text] state with mass between [Formula: see text] and [Formula: see text] GeV.