On Narrow Nucleon Excitation N*(1685)

TL;DR

This paper discusses the potential existence of a narrow nucleon resonance, N*(1685), suggested by recent eta photoproduction data, which cannot be explained by known wide resonances and may indicate an exotic baryon state.

Contribution

It provides an analysis of recent high-precision data suggesting the possible existence of a narrow N*(1685) resonance with small photocoupling, challenging existing resonance models.

Findings

Data cannot be explained by known wide resonances.

Evidence suggests a narrow N*(1685) resonance.

Possible indication of an exotic baryon state.

Abstract

We collected notes and simple estimates about putative narrow nucleon N*(1685) - the candidate for the non-strange member of the exotic anti-decuplet of baryons. In particular, we consider the recent high precision data on eta photoproduction off free proton obtained by the Crystal Ball Collaboration at MAMI. We show that it is difficult to describe peculiarities of these new data in the invariant energy interval of W ~ 1650-1750 MeV in terms of known wide resonances. Using very simple estimates, we show that the data may indicate an existence of a narrow N*(1685) with small photocoupling to the proton.