  LHC searches for missing transverse energy in association with a jet allow to
place strong bounds on the interactions between dark matter and quarks. In this
article, we present an extension of the POWHEG BOX capable of calculating the
underlying cross sections at the next-to-leading order level. This approach
enables us to consistently include the effects of parton showering and to apply
realistic experimental cuts. We find significant differences from a fixed-order
analysis that neglects parton showering effects. In particular, next-to-leading
order corrections do not lead to a significant enhancement of the mono-jet
cross section once a veto on additional jets is imposed. Nevertheless, these
corrections reduce the theoretical uncertainties of the signal prediction and
therefore improve the reliability of the derived bounds. We present our results
in terms of simple rescaling factors, which can be directly applied to existing
experimental analyses and discuss the impact of changing experimental cuts.
