Double Spin Correlations in the Reaction dd → pnpn and in the pn-Elastic Scattering

An unexpectedly large double spin correlation with a sharp dependence on energy, found in elastic proton-proton scattering at large angles in the c.m.s. energy range $$\sqrt {{{s}_{{pp}}}} = 3 - 5.5$$ GeV, may be associated with the formation of exotic octoquark resonances at the thresholds of the strangeness and charm production. For a deeper understanding of the dynamics of this process it is important to measure double spin asymmetry in elastic $$pn$$ scattering in the same kinematics. A possibility of obtaining such data from the reaction $$dd \to pnpn$$ with two polarized deuteron beams on NICA SPD is considered in this paper.