The narrow width of the \Theta^+ - a possible explanation

Abstract

The narrow width of the exotic narrow baryon resonance $\Theta^+$ might be explained by mixing between the two nearly degenerate states that arise in models with two diquarks and an antiquark. The only open $\Theta^+$ decay channel is $KN$. When two states both coupled to a single dominant decay mode are mixed by the loop diagram via this decay mode, diagonalization of the loop diagram decouples one mass eigenstate from this decay mode as in some treatments of the $\rho-\pi$ decay from the mixed singlet-octet $\omega-\phi$ system, the $K^* -\pi$ decay of the strange axial vector mesons and the $NK$ couplings of some baryons. This mechanism can explain the narrow width and weak coupling of $\Theta^+ \to KN$ while allowing a relatively large production cross section from $K^*$ exchange. Interesting tests are suggested in $K^-p$ reactions where backward kaon production must go by exotic baryon exchange.