Neutron anomaly inγN→ηNand the flavour SU(3) symmetry

Abstract

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 ρ 0 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 ss 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.

Scrutinizing the evidence for N(1685)

“…The photocouplings of N (1650)1/2 − are strongly influenced by the ΛK and ΣK thresholds, it may hence be more appropriate to use the "undressed" K-matrix photocoupling. Using the formulae given in [27] we find from the K-matrix couplings that the branching ratio for N (1650)1/2 − → φN vanishes when the N ω coupling has about half the strength of the N ρ coupling.…”

“…In [27] it is argued that the T-matrix photocouplings of N (1650)1/2 − for protons and neutrons imply that N (1650)1/2 − must have a very large φN coupling. The photocouplings of N (1650)1/2 − are strongly influenced by the ΛK and ΣK thresholds, it may hence be more appropriate to use the "undressed" K-matrix photocoupling.…”