The Nπ^{0}π^{0} decays of positive-parity N^{*} and Δ^{*} resonances at about 2 GeV are studied at ELSA by photoproduction of two neutral pions off protons. The data reveal clear evidence for several ...intermediate resonances: Δ(1232), N(1520)3/2^{-}, and N(1680)5/2^{+}, with spin parities J^{P}=3/2^{+}, 3/2^{-}, and 5/2^{+}. The partial wave analysis (within the Bonn-Gatchina approach) identifies N(1440)1/2^{+} and the N(ππ)_{S wave} (abbreviated as Nσ here) as further isobars and assigns the final states to the formation of nucleon and Δ resonances and to nonresonant contributions. We observe the known Δ(1232)π decays of Δ(1910)1/2^{+}, Δ(1920)3/2^{+}, Δ(1905)5/2^{+}, Δ(1950)7/2^{+}, and of the corresponding spin-parity series in the nucleon sector, N(1880)1/2^{+}, N(1900)3/2^{+}, N(2000)5/2^{+}, and N(1990)7/2^{+}. For the nucleon resonances, these decay modes are reported here for the first time. Further new decay modes proceed via N(1440)1/2^{+}π, N(1520)3/2^{-}π, N(1680)5/2^{+}π, and Nσ. The latter decay modes are observed in the decay of N^{*} resonances and at most weakly in Δ^{*} decays. It is argued that these decay modes provide evidence for a 3-quark nature of N^{*} resonances rather than a quark-diquark structure.
We investigate few-boson systems with resonant interactions in a narrow harmonic trap within an effective theory framework. The size of the model space is identified with the effective theory cutoff. ...In the universal regime, the interactions of the bosons can be approximated by contact interactions. We investigate the convergence properties of genuine and smeared contact interactions as the size of the model space is increased and present a detailed error analysis. The spectra for few-boson systems with up to six identical particles are calculated by combining extrapolations in the cutoff and in the smearing parameter.
We present a lattice QCD investigation of the
ρ
-meson with
N
f
=
2
+
1
+
1
dynamical quark flavours for the first time. The calculation is performed based on gauge configuration ensembles produced ...by the ETM Collaboration with three lattice spacing values and pion masses ranging from 230 to 500 MeV. Applying the Lüscher method phase-shift curves are determined for all ensembles separately. Assuming a Breit–Wigner form, the
ρ
-meson mass and width are determined by a fit to these phase-shift curves. Mass and width combined are then extrapolated to the chiral limit, while lattice artefacts are not detectable within our statistical uncertainties. For the
ρ
-meson mass extrapolated to the physical point we find good agreement with experiment. The corresponding decay width differs by about two standard deviations from the experimental value.
Baryonic excitation spectra, electroweak and strong decay properties are discussed within a relativistically covariant constituent quark model based on the instantaneous approximation to the ...three-body Bethe-Salpeter equation.
Electroweak form factors of non-strange baryons Merten, D.; Löring, U.; Kretzschmar, K. ...
The European physical journal. A, Hadrons and nuclei,
8/2002, Letnik:
14, Številka:
4
Journal Article
The resonance spectra of light flavoured baryons show striking near degeneracies which hint at an approximate classification of the resonances into selected
SU
(6) multiplets.
The effective quark interaction in a relativistically covariant constituent quark model based on the Salpeter equation is supplemented by an extra-phenomenological flavour-dependent force in order to ...account for some discrepancies mainly in the description of excited negative-parity
Δ
resonances. Simultaneously an improved description of some other features of the light-flavoured baryon mass spectrum and of some electromagnetic form factors is obtained.
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