The experiment utilizing the active beam dump combined with the  missing energy approach for the searches  of   invisible decays of dark photons  (A') with the mixing strength 10^-5 < ε < 10^-3 and masses M_A' < 100 MeV,  invisible decays of (pseudo)scalar mesons, in particular K_S ,  K_L -> invisible, and hadron and muon interactions resulting in invisible final states due to production of new penetrating particles.