A possibility to determine the P-parity of the ${\Theta }^{+}$ pentaquark in the $pn\to {\Lambda }^0{\Theta }^{+}$ reaction

Abstract

Spin structure of the reaction $\vec{p}\vec{n}\to {\vec{\Lambda }}^0\vec{\Theta }$ is analysed at the threshold in a model independent way under assumption that the ${\Theta }^{+}$ is an isosinglet. We found that the sign of the spin-spin correlation parameter $C_{x,x}$ being measured in a double-spin experiment, determines the P-parity of the ${\Theta }^{+}$ unambiguously. Furthermore we show that the polarization coefficients $K_x^x,K_y^y$ and $K_z^z$ which describe the polarization transfer from polarized beam or target to the final ${\Lambda }^0$ and ${\Theta }^{+}$ are nonzero for a positive parity of the ${\Theta }^{+}$ and equal zero for a negative parity. It allows one to determine the P-parity of the ${\Theta }^{+}$ in a single-spin measurement, since the polarization of the ${\Lambda }^0$ can be measured via its decay ${\Lambda }^0\to {\pi }^{-}+p$.

Comments: 8 pages, Latex . The spin 3/2 of the ${\Theta }^{+}$ and a discrimination for the isospin T=0,1 and 2 are briefly discussed; minor corrections are performed