  We study collider signatures of a class of dark matter models with a
GeV-scale dark Z'. At hadron colliders, the production of dark matter particles
naturally leads to associated production of the Z', which can appear as a
narrow jet after it decays hadronically. Contrary to the usual mono-jet signal
from initial state radiation, the final state radiation of dark matter can
generate the signature of a mono-Z' jet plus missing transverse energy.
Performing a jet-substructure analysis to tag the Z' jet, we show that these Z'
jets can be distinguished from QCD jets at high significance. Compared to
mono-jets, a dedicated search for mono-Z' jet events can lead to over an order
of magnitude stronger bounds on the interpreted dark matter-nucleon scattering
cross sections.
