Search for dark matter in events with aZboson and missing transverse momentum inppcollisions ats=8TeVwith the ATLAS detector

A search is presented for production of dark-matter particles recoiling against a leptonically decaying $Z$ boson in $20.3\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of $pp$ collisions at $\sqrt{s}=8\text{ }\text{ }\mathrm{TeV}$ with the ATLAS detector at the Large Hadron Collider. Events with large missing transverse momentum and two oppositely charged electrons or muons consistent with the decay of a $Z$ boson are analyzed. No excess above the Standard Model prediction is observed. Limits are set on the mass scale of the contact interaction as a function of the dark-matter particle mass using an effective field theory description of the interaction of dark matter with quarks or with $Z$ bosons. Limits are also set on the coupling and mediator mass of a model in which the interaction is mediated by a scalar particle.