Phenomenological study for the Theta+ and two-meson coupling

Abstract

We examine several assignments of spin and parity for the pentaquark Theta+ state (J^P=1/2^{+,-}, 3/2^{+,-}) in connection with phenomenology of known baryon resonances, using a general framework based on the flavor symmetry. Assuming that the Theta+ belongs to an antidecuplet representation which mixes with an octet, we calculate the mass spectra of the flavor partners of the Theta+ based on the SU(3) symmetry. The decay widths of the Theta+ 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 J^P=3/2^-, together with other nonexotic resonances of J^P=3/2^-. The decay widths of Theta -> KN, N(1520) -> pi N, and N(1700) -> pi N are also reproduced simultaneously. We then evaluate two-meson couplings of Theta+, using experimental information of nucleon partners decaying into pi pi N channels, in which the two pions are in scalar- and vector-type correlations. We examine two assignments of spin and parity J^P=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 pi- p -> K- Theta+ and K+ p -> pi+ Theta+ are calculated. Substantial interference of two terms may occur in the reaction processes for the J^P=1/2^+ case, whereas the interference effect is rather small for the 3/2^- case.