Properties of nucleon and $Delta$ resonances are derived from a multichannel partial wave analysis. The statistical significance of pion and photo-induced inelastic reactions off protons are studied in a multichannel partial-wave analysis.
Evidence is reported for two nucleon resonances with spin-parity $J^P=1/2^-$ and $J^P=3/2^-$ at a mass just below 1.9,GeV. The evidence is derived from a coupled-channel analysis of a large number of pion and photo-produced reactions. The two resonan
ces are nearly degenerate in mass with two resonances of the same spin but positive parity. Such parity doublets are predicted in models claiming restoration of chiral symmetry in high-mass excitations of the nucleon. Further examples of spin parity doublets are found in addition. Alternatively, the spin doublet can be interpreted as member of the 56-plet expected in the third excitation band of the nucleon. Implications for the problem of the {it missing resonances} are discussed.
Results from a multi-channel partial wave analysis of elastic and inelastic $pi N$ and $gamma N$ induced reactions are presented. The analysis evidences the existence of a spin-quartet of nucleon resonances with total angular momenta $J^P=1/2^+,...,
7/2^+$. All states fall into a $pm130$,MeV mass gap centered at 1.97,GeV. The spin quartet is at variance with S-wave diquark configurations required in classical di-quark models.
The reactions $gamma p rightarrow K^{+}Sigma^{pm}pi^{mp}$ were studied with the SAPHIR detector using a tagged photon beam at the electron stretcher facility ELSA in Bonn. The decays $Sigma^{-} rightarrow npi^{-}$ and $Sigma^{+} rightarrow npi^{+}, p
pi^0$ were fully reconstructed. Reaction cross sections were measured as a function of the photon energy from threshold up to $2.6,$GeV with considerably improved statistics compared to a previous bubble chamber measurement. The cross sections rise monotonously with increasing photon energy. The two-particle mass distributions of $Sigma^{pm}pi^{mp}$ and $K^+pi^-$ show substantial production of resonant states.
The reaction $gamma pto ppi^0eta$ has been studied with the CBELSA detector at the tagged photon beam of the Bonn electron stretcher facility. The reaction shows contributions from $Delta^+(1232)eta$, $N(1535)^+pi^0$ and $pa_0(980)$ as intermediate s
tates. A partial wave analysis suggests that the reaction proceeds via formation of six $Delta$ resonances, $Delta(1600)P_{33}$, $Delta(1920)P_{33}$, $Delta(1700)D_{33}$, $Delta(1940)D_{33}$, $Delta(1905)F_{35}$, $Delta(2360)D_{33}$, and two nucleon resonances $N(1880)P_{11}$ and $N(2200)P_{13}$, for which pole positions and decay branching ratios are given.
Evidence is reported for the existence of a parity doublet of Delta resonances with total angular momentum J=3/2 from photoproduction of the p pi^0 eta final state. The two parity partners Delta(1920)P_{33} and Delta(1940)D_{33} make significant cont
ributions to the reaction. Cascades of resonances into Delta(1232) eta, N(1535) pi, and N a_0(980) are clearly observed.
