Search for invisible particles produced in association with single-top-quarks in proton-proton collisions at $\sqrt{s}$ = 8 TeV with the ATLAS detector

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 $\sqrt{s}=\mathrm {8~TeV}$ 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.