  Search for invisible final states produced at the Large Hadron Collider (LHC)
by new physics scenarios are normally carried out resorting to a variety of
probes emerging from the initial state, in the form of single-jet, -photon and
-$Z$ boson signatures. These are particularly effective for models of
Supersymmetry (SUSY) in presence of $R$-parity conservation, owing to the
presence in their spectra of a stable neutralino as dark matter candidate. We
assume here as theoretical framework Supersymmetric ($B-L$) extension of the
Standard Model (BLSSM), wherein a mediator for invisible decays can be $Z'$
boson. The peculiarity of the signal is thus that the final state objects carry
a very large (transverse) missing energy, since the $Z'$ is naturally massive
and constrained by direct searches and electro-weak precision tests to be at
least in TeV scale region. Under these circumstances the efficiency in
accessing the invisible final state and rejecting the standard model background
is very high. This somehow compensates the rather meagre production rates.
Another special feature of this invisible BLSSM signal is its composition,
which is often dominated by sneutrino decays (alongside the more traditional
neutrino and neutralino modes). Sensitivity of the CERN machine to these two
features can therefore help disentangling the BLSSM from more popular SUSY
models. We assess in this analysis the scope of the LHC in establishing the
aforementioned invisible signals through a sophisticated signal-to-background
simulation carried out in presence of parton shower, hadronisation and detector
effects. We find that significant sensitivity exists already after 300
fb$^{-1}$ during Run 2. We find that mono-jet events can be readily accessible
at the LHC, so as to enable one to claim a prompt discovery, while mono-photon
and -$Z$ signals can be used as diagnostic tools of the underlying scenario.

High Energy Physics - Phenomenology