Spin observables in the $NN\to YΘ^+$ reaction at the threshold and quantum numbers of the $Θ^+$ 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 $N N\to Y Θ^+$ at the threshold for an arbitrary spin of the pentaquark $Θ^+$. 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 $Θ^+$ unambiguously and independently on the spin of the $Θ^+$. Measurement of these spin observables in the both $pp$- and $pn$- channels of this reaction determines also the isospin of the $Θ^+$.