  We present strong experimental evidence for the existence of a nonstrange
$\it NN$-decoupled dibaryon with a mass of about 1956 MeV stable against strong
decay, which is a very likely candidate for long-sought multiquark hadrons with
the baryon number B=2. We start by presenting the first evidence for the
existence of this dibaryon called $d^{\ast }_{1}$(1956), that was found in the
energy spectrum of coincident photons emitted at $\pm 90^0$ from the reaction
$pp \to pp \gamma\gamma$ at an energy of 216 MeV measured at JINR. We then show
its signatures found in several experimental energy spectra of single photons
and invariant mass spectra of photon pairs from photon production processes
induced by nucleon-nucleon and nucleon-nucleus collisions at intermediate
energies.
