The reactions γp → π 0 p and γp → π + n are analyzed in a semi-phenomenological approach up to E ∼ 2.3 GeV. Fits to differential cross section and single and double polarization observables are performed. A good overall reproduction of the available photoproduction data is achieved. The Jülich2012 dynamical coupled-channel model -which describes elastic πN scattering and the world data base of the reactions πN → ηN , KΛ, and KΣ at the same time -is employed as the hadronic interaction in the final state. The framework guarantees analyticity and, thus, allows for a reliable extraction of resonance parameters in terms of poles and residues. In particular, the photocouplings at the pole can be extracted and are presented.

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The analytic properties of scattering amplitudes provide important information. Besides the cuts, the poles and zeros on the different Riemann sheets determine the global behavior of the amplitude on the physical axis. Pole positions and residues allow for a parameterization of resonances in a well-defined way, free of assumptions for the background and energy dependence of the resonance part. This is a necessary condition to relate resonance contributions in different reactions. In the present study, we determine the pole structure of pion-nucleon scattering in an analytic model based on meson exchange. For this, the sheet structure of the amplitude is determined. To show the precision of the resonance extraction and discuss phenomena such as resonance interference, we discuss the S 11 amplitude in greater detail.

Elastic πN scattering and the world data of the family of reactions π − p → ηn, K 0 Λ, K 0 Σ 0 , K + Σ − , and π + p → K + Σ + are described simultaneously in an analytic, unitary, coupled-channel approach. SU(3) flavor symmetry is used to relate both the t-and the u-channel exchanges that drive the meson-baryon interaction in the different channels. Angular distributions, polarizations, and spin-rotation parameters are compared with available experimental data. Partial-wave amplitudes are determined and the resonance content is extracted from the analytic continuation, including resonance positions and branching ratios, and possible sources of uncertainties are discussed. The results provide the final-state interactions for the ongoing analysis of photo-and electroproduction data.

The isospin I = 0 and I = 1 kaon-nucleon S, P , D, F wave phase shifts are studied in the chiral SU(3) quark model by solving the resonating group method (RGM) equation. The calculated phase shifts for different partial waves are in agreement with the experimental data. Furthermore, the structures of the ∆K states with L = 0, I = 1 and I = 2 are investigated. We find that the interaction between ∆ and K in the case of L = 0, I = 1 is attractive, which is not like the situation of the N K system, where the S-wave interactions between N and K for both I = 0 and I = 1 are repulsive. Our numerical results also show that when the model parameters are taken to be the same as in our previous N N and Y N scattering calculations, the ∆K state with L = 0 and I = 1 is a weakly bound state with about 2 MeV binding energy, while the one with I = 2 is unbound in the present one-channel calculation.

Abstract. Quasi-free photoproduction of η -mesons off nucleons bound in the deuteron has been measured with the combined Crystal Barrel -TAPS detector. The experiment was done at a tagged photon beam of the ELSA electron accelerator in Bonn for incident photon energies from the production threshold up to 2.5 GeV. The η -mesons have been detected in coincidence with recoil protons and recoil neutrons. The quasi-free proton data are in good agreement with the results for free protons, indicating that nuclear effects have no significant impact. The coincidence with recoil neutrons provides the first data for the γn → nη reaction. In addition, also first estimates for coherent η -production off the deuteron have been obtained. In agreement with model predictions, the total cross-section for this channel is found to be very small, at most at the level of a few nb. The data are compared to model calculations taking into account contributions from nucleon resonances and t-channel exchanges.

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We confirm our previous prediction of a d * state with I(J P ) = 0(3 + ) [Phys. Rev. C 60, 045203 (1999)] and report for the first time based on a microscopic calculation that d * has about 2/3 hidden color (CC) configurations and thus is a hexaquark-dominated exotic state. By performing a more elaborate dynamical coupled-channels investigation of the ∆∆-CC system within the framework of resonating group method (RGM) in a chiral quark model, we found that the d * state has a mass of about 2.38 − 2.42 GeV, a root-mean-square radius (RMS) of 0.76 − 0.88 fm, and a CC fraction of 66% − 68%. The last may cause a rather narrow width to d * which, together with the quantum numbers and our calculated mass, is consistent with the newly observed resonance-like structure (M ≈ 2380 MeV, Γ ≈ 70 MeV) in double-pionic fusion reactions reported by WASA-at-COSY Collaboration.PACS numbers: 14.20. Pt, 13.75.Cs, 12.39.Jh, 24.10.Eq The ABC effect has drawn physicists' great attention since its observation in 1961 in the pd reaction [1]. In recent years, much experimental progress in exploring the nature of the ABC effect has been made. In 2009, the CELSIUS/WASA Collaboration measured the most basic double-pionic fusion reaction pn → dπ 0 π 0 with an incident proton energy of 1.03 GeV and 1.35 GeV [2], and found significant enhancements in the ππ invariant mass spectrum at ππ invariant mass below 0.32 GeV 2 and also in the dπ invariant mass spectrum at ∆ resonance region. To accommodate these data as well as the energy dependence of the total cross section at √ s < 2.5 GeV, the conventional t-channel ∆∆ intermediate state is found to be not sufficient, and a new structure, namely an s-channel resonance with mass of about 2.36 GeV and width of about 80 MeV, is expected. In 2011, the WASA-at-COSY Collaboration further measured the pn → dπ 0 π 0 reaction with the beam energies of 1.0−1.4 GeV which cover the transition region of the conventional t-channel ∆∆ process [3]. They found that neither the t-channel ∆∆ process nor the Roper resonance process can explain the data, and an s-channel resonance with quantum numbers of I(J P ) = 0(3 + ), mass of about 2.37 GeV and width of about 70 MeV is indeed needed to describe the data. Recently, the WASA-at-COSY Collaboration measured the polarized np scattering through the quasi-free process dp → p spectator np [4,5]. By incorporating the newly measured A y data into the SAID analysis, they obtained a pole in the 3 D 3 -3 G 3 waves at (2380 ± 10)+ i(40 ±5) MeV, which again supports the existence of a resonance, called d * , as mentioned in Ref. [3]. Further evidence of this resonance has also been reported in the quasi-free np → npπ 0 π 0 reaction [6]. Since its mass is above the threshold of ∆N π channel, while its width is much smaller than the decay width of ∆, this resonance must be a very interesting state involving new physical mechanisms and it is obviously worthwhile investigating.Theoretically, the possibility of the existence of dibaryon states was first proposed in 1964 by Dyson a...