  We discuss a collider probe of a dark sector model in which the dark matter
is charged under a new, hidden $U(1)$ gauge group. In particular, we look for
the so-called Darkstrahlung process, in which the final states dark matter
radiates a new $Z'$ gauge boson and it manifests as dilepton resonances. This
work emphasizes the potential of dilepton final states with missing transverse
energy in probing the darkstrahlung process. We recast the ATLAS Run 2 search
for dilepton resonances in association with missing energy in addition to the
ATLAS and CMS searches for sleptons. We find that the recasted searches put
strong constraints on the coupling between the dark matter and the $Z'$.
Moreover, we evaluate refined search strategies for $Z'$ production and propose
an analysis employing constraints on the lepton invariant mass and higher
missing energy cut related to the darkstrahlung process. Simulation outcomes
indicate substantial enhancements, particularly by a factor of 6 in regions
featuring lower $Z'$ masses. Finally, we also discuss the case when the $Z'$
has a long lifetime, resulting in displaced decay of the boson.
