  We establish a hybrid seesaw mechanism to explain small neutrino masses and
predict cold dark matter candidate in the context of the B-L gauge symmetry
extension of the Standard Model. In this model a new scalar doublet and two new
fermion singlets are introduced at loop-level beyond the minimal Type I seesaw.
The lightest particle inside the loop can be dark matter candidate. We study in
detail the constraints from neutrino oscillation data, lepton flavor violating
processes and cosmological observation. We also explore the predictions of the
decays of the new charged scalars in each spectrum of neutrino masses and show
the most optimistic scenarios to distinguish the spectra. We consider the pair
production of the stable fermion associated with two observable SM charged
leptons at the LHC, which occurs in a two-step cascade decay of the new gauge
boson Z' and the new charged scalars stand as intermediate particles. The
masses of missing dark matter and its parent particle can be well-determined in
such production topology.
