Regular Article - Theoretical Physics
Nucleon resonances in the fourth-resonance region
Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, Bonn, Germany
2 Petersburg Nuclear Physics Institute, Gatchina, Russia
Accepted: 15 November 2011
Published online: 14 December 2011
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.
© SIF, Springer-Verlag Berlin Heidelberg, 2011