EPJ

2021 Impact factor 3.131
EPJ A - Hadrons and Nuclei
Hadrons and Nuclei
Eur. Phys. J. A 3, 171-181

Analysis of eta production using a generalized Lee model

Johannes Denschlag1,2 - Lothar Tiator1 - Dieter Drechsel1

1 Institut für Kernphysik, Johannes Gutenberg Universität Mainz, J.J. Becherweg 45, 55099 Mainz, Germany
2 Institut für Experimentalphysik, Universität Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria

Received: 5 March 1998 / Revised version: 23 June 1998 Communicated by W. Weise

Abstract
We have investigated the processes N($\pi$, $\pi$)N and N($\pi$, $\eta$)N close to eta threshold using a simple, nonrelativistic Lee model which has the advantage of being analytically solvable. It is then possible to study the Riemann sheets of the S-matrix and the behavior of its resonance poles especially close to threshold. A theoretical simulation of the experimental cusp effect at eta threshold leads to a characteristic distribution of poles on the Riemann sheets. We find a pole located in the 4th Riemann sheet that up to now has not been discussed. It belongs to the cusp peak at eta threshold. In addition we obtain the surprising result using the Lee model that the resonance S11(1535) does not play a large role. The main features of the experimental data can be reproduced without explicitly introducing this resonance. Furthermore, we have also studied the reactions N($\gamma$, $\pi$)N and N($\gamma$, $\eta$)N and find reasonable agreement between the data and both models with and without the S11(1535) resonance.

PACS
13.60.Le Meson production - 14.20.Gk Baryon resonances with S = 0 - 13.75.Gx Pion-baryon interactions

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