Nucleon resonances in the fourth-resonance region

Nucleon and Delta 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 1850 MeV, 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 J(P) = 1/2(+), ... , 7/2(+). 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 J = 1/2, ... , 7/2. Just below 1.9 GeV 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.