Strong evidence for nucleon resonances near 1900\,MeV

TL;DR

This paper provides strong evidence for nucleon resonances near 1900 MeV by analyzing photoproduction data and extracting resonance poles using a multichannel model, confirming their existence in this energy region.

Contribution

The study introduces an almost model-independent method to identify nucleon resonance poles near 1900 MeV using multipole analysis and multichannel $L+P$ modeling.

Findings

Confirmed existence of nucleon resonance poles at about 1.9 GeV.

Identified multiple resonance states with specific spin-parity assignments.

Used a novel combination of multipole extraction and multichannel analysis.

Abstract

Data on the reaction $\gamma p\to K^+\Lambda$ from the CLAS experiments are used to derive the leading multipoles, $E_{0+}$, $M_{1-}$, $E_{1+}$, and $M_{1+}$, from the production threshold to 2180\,MeV in 24 slices of the invariant mass. The four multipoles are determined without any constraints. The multipoles are fitted using a multichannel $L+P$ model which allows us to search for singularities and to extract the positions of poles on the complex energy plane in an almost model-independent method. The multipoles are also used as additional constraints in an energy-dependent analysis of a large body of pion and photo-induced reactions within the Bonn-Gatchina (BnGa) partial wave analysis. The study confirms the existence of poles due to nucleon resonances with spin-parity $J^P = 1/2^-; 1/2^+$, and $3/2^+$ in the region at about 1.9\,GeV.