We present a pion photoproduction model on the free nucleon based on an Effective Lagrangian Approach (ELA) which includes the nucleon resonances ($\Delta(1232)$, N(1440), N(1520), N(1535), $\Delta (1620)$, N(1650), and $\Delta (1700)$), in addition to Born and vector meson exchange terms. The model incorporates a new theoretical treatment of spin-3/2 resonances, first introduced by Pascalutsa, avoiding pathologies present in previous models. Other main features of the model are chiral symmetry, gauge invariance, and crossing symmetry. We use the model combined with modern optimization techniques to assess the parameters of the nucleon resonances on the basis of world data on electromagnetic multipoles. We present results for electromagnetic multipoles, differential cross sections, asymmetries, and total cross sections for all one pion photoproduction processes on free nucleons. We find overall agreement with data from threshold up to 1 GeV in laboratory frame.Comment: Misprints corrected. 60 pages. 33 figures.5 tables. Accepted for publication in Annals of Physics (NY

Mapping states with explicit gluonic degrees of freedom in the light sector is a challenge, and has led to controversies in the past. In particular, the experiments have reported two different hybrid candidates with spin-exotic signature, π1(1400) and π1 (1600), which couple separately to ηπ and η π. This picture is not compatible with recent Lattice QCD estimates for hybrid states, nor with most phenomenological models. We consider the recent partial wave analysis of the η ( ) π system by the COMPASS collaboration. We fit the extracted intensities and phases with a coupled-channel amplitude that enforces the unitarity and analyticity of the S-matrix. We provide a robust extraction of a single exotic π1 resonant pole, with mass and width 1564 ± 24 ± 86 MeV and 492 ± 54 ± 102 MeV, which couples to both η ( ) π channels. We find no evidence for a second exotic state. We also provide the resonance parameters of the a2(1320) and a 2 (1700).

The first CLAS12 experiments will provide high-precision data on inclusive electron scattering observables at a photon virtuality Q 2 ranging from 0.05 GeV 2 to 12 GeV 2 and center-of-mass energies W up to 4 GeV. In view of this endeavour, we present the modeling of the resonant contributions to the inclusive electron scattering observables. As input, we use the existing CLAS electrocoupling results obtained from exclusive meson electroproduction data off protons, and evaluate for the first time the resonant contributions based on the experimental results on the nucleon resonance electroexcitation. The uncertainties are given by the data and duly propagated through a Monte Carlo approach. In this way, we obtain estimates for the resonant contributions, important for insight into the nucleon parton distributions in the resonance region and for the studies of quarkhadron duality.

We present a unitary multichannel model forKN scattering in the resonance region that fulfills unitarity. It has the correct analytical properties for the amplitudes once they are extended to the complex-s plane and the partial waves have the right threshold behavior. To determine the parameters of the model, we have fitted single-energy partial waves up to J = 7/2 and up to 2.15 GeV of energy in the center-of-mass reference frame obtaining the poles of the Λ * and Σ * resonances, which are compared to previous analyses. We provide the most comprehensive picture of the S = −1 hyperon spectrum to date. Important differences are found between the available analyses making the gathering of further experimental information onKN scattering mandatory to make progress in the assessment of the hyperon spectrum.