Polarization observables in the processes $p+p\to \Theta^+ +\Sigma^+$ and $n+p\to \Theta^+ +\Lambda^0$, for any spin and parity of the $\Theta^+$-hyperon in the threshold region

Abstract

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 a model independent way, which applies to any spin and parity of the $\Theta^+$-hyperon in the near threshold region. 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.