Spin observables in the $NN\to Y\Theta^+$ reaction at the threshold and quantum numbers of the $\Theta^+$ pentaquark

Abstract

General formulae for the spin-spin correlation parameters $C_{i,j}$ and spin-transfer coefficients $K_i^j$ are derived for the reaction $N N\to Y \Theta^+$ at the threshold for an arbitrary spin of the pentaquark $\Theta^+$. It is shown that a measurement of the sign of $C_{y,y}$ or an observation of the non-zero polarization transfer from the nucleon to the hyperon $Y$ allow one to determine the P-parity of the $\Theta^+$ unambiguously and independently on the spin of the $\Theta^+$. Measurement of these spin observables in the both $pp$- and $pn$- channels of this reaction determines also the isospin of the $\Theta^+$.