Phenomenological Study for the Θ and Two-meson Coupling

We examine several assignments of spin and parity for the pentaquark Θ state (JP = 1/2, 3/2) in connection with phenomenology of known baryon resonances, using a general framework based on the flavor symmetry. Assuming that the Θ belongs to an antidecuplet representation which mixes with an octet, we calculate the mass spectra of the flavor partners of the Θ based on the SU(3) symmetry. The decay widths of the Θ and nucleon partners are analyzed for the consistency check of the mixing angle obtained from the masses. It is found that a suitable choice of the mixing angle successfully reproduces the observed masses of exotics, when their spin and parity are assigned to be JP = 3/2, together with other nonexotic resonances of JP = 3/2. The decay widths of Θ → KN , N(1520) → πN , and N(1700) → πN are also reproduced simultaneously. We then evaluate two-meson couplings of Θ, using experimental information of nucleon partners decaying into ππN channels, in which the two pions are in scalarand vector-type correlations. We examine two assignments of spin and parity JP = 1/2 and 3/2, for which the experimental spectra of known resonances with exotic baryons are properly reproduced by an octet-antidecuplet representation mixing scheme. Using the obtained coupling constants, total cross sections of the reactions πp → KΘ and Kp → πΘ are calculated. Substantial interference of two terms may occur in the reaction processes for the JP = 1/2 case, whereas the interference effect is rather small for the 3/2 case.