  The PADME experiment is searching for the Dark Photon $A'$ in the $e^{+}e^{-}
\to \gamma A'$ process, assuming a $A'$ decay into invisible particles. In
extended Dark Sector models, a Dark Higgs $h'$ can be produced alongside $A'$
in the process $e^{+}e^{-} \to h' A'$. If the $h'$ mass is greater than twice
the $A'$ mass the final state will be composed by three $e^{+}e^{-}$ pairs.
Such extremely rare process is explorable by the PADME experiment, which could
get a first measure and impose limits on models of physics beyond the Standard
Model.
