The neutron anomaly in the gamma N --> eta N cross section through the looking glass of the flavour SU(3) symmetry

Abstract

We study the implications of the flavour SU(3) symmetry for various interpretations of the neutron anomaly in the ${\hat{I}}^{3}N\to \hat{I}\cdot N$ cross section. We show that the explanation of the neutron anomaly due to interference of known N(1535) and N(1650) resonances implies that N(1650) resonance should have a huge coupling to $\ddot{I}•$-meson -- at least 5 times larger than the corresponding $\ddot{I}{}^0$ coupling. In terms of quark degrees of freedom this means that the well-known N(1650) resonance must be a "cryptoexotic pentaquark"-- its wave function should contain predominantly an $s\bar{s}$ component. It turns out that the "conventional" interpretation of the neutron anomaly by the interference of known resonances metamorphoses into unconventional physics picture of N(1650).

8 pages, 1 figure