Eur. Phys. J. A (2011) 47: 153
https://doi.org/10.1140/epja/i2011-11153-9

Regular Article - Theoretical Physics

Nucleon resonances in the fourth-resonance region

¹ Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, Bonn, Germany
² Petersburg Nuclear Physics Institute, Gatchina, Russia

Received: 17 September 2011
Accepted: 15 November 2011
Published online: 14 December 2011

Abstract

Nucleon and resonances in the fourth-resonance region are studied in a multichannel partial-wave analysis which includes nearly all available data on pion- and photo-induced reactions off protons. In the high-mass range, above 1850MeV, several alternative solutions yield a good description of the data. For these solutions, masses, widths, pole residues and photocouplings are given. In particular, we find evidence for nucleon resonances with spin-parities . For one set of solutions, there are four resonances forming naturally a spin-quartet of resonances with orbital angular momentum L = 2 and spin S = 3/2 coupling to . Just below 1.9GeV we find a spin doublet of resonances with J ^P = 1/2^- and 3/2^- . Since a spin partner with J ^P = 5/2^- is missing at this mass, the two resonances form a spin doublet which must have a symmetric orbital-angular-momentum wave function with L = 1 . For another set of solutions, the four positive-parity resonances are accompanied by mass-degenerate negative-parity partners --as suggested by the conjecture of chiral symmetry restoration. The possibility of a J ^P = 1/2⁺, 3/2⁺ spin doublet at 1900MeV belonging to a 20-plet is discussed.