Neutron anomaly in γN → ηN and the flavour SU(3) symmetry

Abstract

We study the implications of the flavour SU(3) symmetry for various interpretations (existence of a narrow anti-decuplet resonance, interference of known resonances and a cusp effect) of the neutron anomaly in γN → ηN 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 ϕ-meson – at least 5 times larger than the corresponding ρ0 coupling. In terms of quark degrees of freedom that implies that the well-known N(1650) resonance must be a “cryptoexotic pentaquark”– its wave function should contain predominantly an ss̄ component, implying that the N(1650) resonance is dominantly a pentaquark. The explanation of the neutron anomaly as a cusp effect implies very strong violation of the flavour SU(3) symmetry.