Photoproduction of theΘ+resonance on the nucleon in a Regge model

Abstract

We estimate the reaction mechanisms for the photoproduction of the ${\ensuremath{\Theta}}^{+}(1540)$ resonance on the nucleon, through $K$ and ${K}^{*}$ Regge exchanges. We compare the size of the cross sections for the $\ensuremath{\gamma}n\ensuremath{\rightarrow}{K}^{\ensuremath{-}}{\ensuremath{\Theta}}^{+}$ and $\ensuremath{\gamma}p\ensuremath{\rightarrow}{\overline{K}}^{0}{\ensuremath{\Theta}}^{+}$ reactions and investigate their sensitivity to the spin-parity assignments ${J}^{P}={\frac{1}{2}}^{\ifmmode\pm\else\textpm\fi{}},{\frac{3}{2}}^{\ifmmode\pm\else\textpm\fi{}}$ for the ${\ensuremath{\Theta}}^{+}$ resonance. The model allows one to estimate the cross sections corresponding with a given upper bound on the width of the ${\ensuremath{\Theta}}^{+}$. Within this model, the cross sections on the neutron are found to be around a factor of 5 larger than the ones on the proton, due to the presence of charged $K$ exchange for the reaction on a neutron target. Furthermore, the photon asymmetry is found to display a pronounced sensitivity to the parity of the ${\ensuremath{\Theta}}^{+}$, making it a very promising observable to help determine the quantum numbers of the ${\ensuremath{\Theta}}^{+}$ resonance.