Photo-production of the pentaquark $Θ^{+}$ with positive and negative parities

Abstract

We investigate the production of the pentaquark $Θ^+$ baryon via the $γn\to K^-Θ^+$ and $γp\to \bar{K}^0 Θ^+$ processes, focusing on the parity of the $Θ^+$. Using the effective Lagrangians, we calculate the total and differential cross sections with the spin of the $Θ^+$ presumed to be 1/2. We employ the coupling constant of the $KNΘ$ vertex determined by assuming its mass and the decay width to be $1540 {\rm MeV}$ and $15 {\rm MeV}$. That of the $K^*NΘ$ is taken to be about a half of the $KNΘ$ coupling constant. We estimate the cutoff parameter by reproducing the total cross section of the $γp \to K^+ Λ$ reaction. It turns out that the total cross section for the $γn\to K^- Θ^+$ process is about four times larger than that of the $γp\to\bar{K}^0Θ^+$. We also find that the cross sections for the production of the positive-parity $Θ$ are about ten times as large as those for the negative-parity ones.