Polarization observables in the processes

Using the symmetry properties of the strong interaction, such as the Pauli principle, the P-invariance, the conservation of the total angular momentum and isotopic invariance, we establish the spin structure of the threshold matrix elements for the processes $p + p\to \Theta^ + + \Sigma^ + $ and $n + p\to \Theta^ + + \Lambda^0$, in the near-threshold region, in a model-independent way, which applies to any spin and parity of the $\Theta^ + $-hyperon. We predict the double-spin observables for these processes, such as the dependence of the differential cross-section on the polarizations of the colliding nucleons, and the coefficients of polarization transfer from a nucleon beam or target to the produced $\Sigma^ + $- or $\Lambda^0$-hyperon. We prove that these observables are sensitive to the P-parity of the $\Theta^ + $-baryon, for any value of its spin. As an example of dynamical considerations, we analyzed these reactions in the framework of K-meson exchange