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

Abstract

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

Comments: 11 figures, 10 pages. Will be submitted to Phys. Rev. D