Nucleon resonances in the fourth resonance region

Nucleon and $\mathrm{\Delta }$ 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 photo-couplings are given. In particular, we find evidence for nucleon resonances with spin-parities $J^P=1\mathrm{/}{2}^{+}\mathrm{.}\mathrm{.}.7\mathrm{/}{2}^{+}$. 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 $J=1\mathrm{/}2,\mathrm{.}\mathrm{.}\mathrm{.},7\mathrm{/}2$. Just below 1.9,GeV we find a spin doublet of resonances with $J^P=1\mathrm{/}{2}^{-}$ and $3\mathrm{/}{2}^{-}$. Since a spin partner with $J^P=5\mathrm{/}{2}^{-}$ 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 1900,MeV belonging to a 20-plet is discussed.