Evidence for a negative-parity spin-doublet of nucleon resonances at 1.88\,GeV

Abstract

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 resonances 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.

10 pages, 3 figures, 4 tables, minor revision

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• Symmetries of hadrons after unbreaking the chiral symmetry
• Pion- and photo-induced transition amplitudes to $\Lambda K$, $\Sigma K$, and $N\eta$
• Chiral Symmetry Breaking on the Lattice
• Effects of $N(2000)5/2^{+}$, $N(2060)5/2^{-}$, $N(2120)3/2^{-}$, and $N(2190)7/2^{-}$ on $K^{\ast }\Lambda$ photoproduction
• Evidence for a spin-quartet of nucleon resonances at 2\,GeV
• Sign ambiguity in the K Sigma channel
• Measurement of polarisation observables in $K_s^0{\Sigma }^{+}$ photoproduction off the proton
• Why is GeV physics relevant in the age of the LHC?
• SPQR -- Spectroscopy: Prospects, Questions & Results