Extraction of P11 resonances from pi N data

TL;DR

This study confirms the stability of two P11 nucleon resonance poles near the pi Delta threshold across various models, emphasizing the need for more precise pi N data to improve resonance extraction accuracy.

Contribution

The paper demonstrates the robustness of two P11 resonance poles against model variations and explores the potential for multiple poles in the 1.5-2 GeV region, providing refined resonance parameters.

Findings

Two P11 resonance poles are stable across models.

The number of poles in the 1.5-2 GeV region may vary.

More accurate pi N data are needed for precise resonance determination.

Abstract

We show that two P11 nucleon resonance poles near the pi Delta threshold, obtained in several analyses, are stable against large variations of parameters within a dynamical coupled-channels analysis based on meson-exchange mechanisms. By also performing an analysis based on a model with a bare nucleon state, we find that this two-pole structure is insensitive to the analytic structure of the amplitude in the region below pi N threshold. Our results are M_pole = (1363^{+9}_{-6} -i79^{+3}_{-5}) MeV and (1373^{+12}_{-10} -i114^{+14}_{-9}) MeV. We also demonstrate that the number of poles in the 1.5 GeV < W < 2 GeV region could be more than one, depending on how the structure of the single-energy solution of SAID is fitted. For three-pole solutions, our best estimated result of a pole near N(1710) listed by Particle Data Group is (1829^{+131}_{-65} -i192^{+88}_{-110}) MeV which is close to the results of several previous analyses. Our results indicate the need of more accurate pi N reaction data in the W > 1.6 GeV region for high precision resonance extractions.