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 eight-quark 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 correlation in elastic $pn$ scattering in the same kinematics. The possibility of obtaining this data from the reaction $dd\to pnp$ with two polarized deuterons on NICA SPD is considered in this paper.