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

TL;DR

This paper explores the neutron anomaly in gamma-induced eta production, proposing that it indicates the N(1650) resonance is a cryptoexotic pentaquark with significant s-sbar content, challenging conventional interpretations.

Contribution

It demonstrates that explaining the neutron anomaly requires N(1650) to have a large phi-meson coupling, suggesting it is a cryptoexotic pentaquark rather than a conventional resonance.

Findings

N(1650) resonance should have a large phi-meson coupling

N(1650) likely has a significant s-sbar component

Conventional resonance interference explanation implies unconventional physics

Abstract

We study the implications of the flavour SU(3) symmetry for various interpretations of the neutron anomaly in the $\gamma N\to\eta N$ 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 $\phi$-meson -- at least 5 times larger than the corresponding $\rho^0$ 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).