New narrow N*(1685) resonance: Review of observations

Abstract

Abstract. The recent Review of Particle Physics [1] includes a new narrow N*(1685) resonance. Its properties, the narrow width ( < 25 MeV) and the strong photoexcitation on the neutron, are unusual. The paper reviews experimental data which have led to the evidence for this resonance. Alternative explanations of the phenomenon at W ∼ 1.685 GeV, namely the interference of well-known resonances and the sub-threshold meson-baryon production, are discussed as well.

Neutron helicity amplitudes

“…In the excitation function of η-photoproduction from neutrons, a narrow structure was observed in a number of experiments [15][16][17][18][19][23][24][25]. The narrow structure was interpreted as N (1685) [77] with preferred quantum numbers J P = 1/2 + and identified with a pentaquark expected in the chiral soliton model [5]. Its properties were determined [15,16] as M = 1670±5 and Γ = 28±5 MeV, respectively, and…”

Highlights of the Spectroscopy of Hyperons and Cascade Baryons

“…The non-strange and strange partners in the anti-decuplet suffer from the difficulty that their identification as members of the anti-decuplet is model-dependent. Evidence for the possible existence of two narrow states at 1685 and 1720 MeV has been reported [72,73,74]. The peak at 1685 MeV is discussed extensively in the literature, see, e.g.,Refs.…”

“…However, in a series of precision experiments, the evidence for pentaquarks has faded away (see, e.g., Ref. [69,70,71]) even though some evidence remains that a narrow state with J P = 1/2 + at 1720 MeV might exist [72,73,74]. High-precision experiments are mandatory to settle this important issue.…”