S. Krewald

Near threshold enhancement of the p p-bar mass spectrum in J/Psi decay

We investigate the nature of the near-threshold enhancement in the pp invariant-mass spectrum of the reaction J/{psi}{yields}{gamma}pp reported recently by the BES Collaboration. Using the Juelich NN model we show that the mass dependence of the pp spectrum close to the threshold can be reproduced by the S-wave pp final state interaction in the isospin I=1 state within the Watson-Migdal approach. However, because of our poor knowledge of the NN interaction near-threshold and of the J/{psi}{yields}{gamma}pp reaction mechanism and in view of the controversal situation in the decay J/{psi}{yields}{pi}{sup 0}pp, where no obvious signs of a pp final state interaction are seen, explanations other than final state interactions cannot be ruled out at the present stage.

Analytic properties of the scattering amplitude and resonances parameters in a meson exchange model

The analytic properties of scattering amplitudes provide i mportant 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 al low for a parameterization of resonances in a well-defined way, f ree of assumptions for the background and energy dependence of the resonance part. This is a necessary condition to relate r esonance 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.

Experimental signatures of the Δ(1236)-hole quenching mechanism in pionic states

Abstract The Δ(1236)-hole model for the quenching of spin-isospin transition strength is investigated by explicitly including the Δ(1236) into the nuclear wave function. The angular momentum dependence of the quenching effect is discussed as a possible experimental signature of the model.

Coupled-channel dynamics in the reactions πN → πN, ηN, KΛ, KΣ

Elastic πN scattering and the world data of the family of reactions π−p → ηn, K0Λ, K0Σ0, 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.

Coupled-channel dynamics in the reactions piN --> piN, etaN, KLambda, KSigma

Elastic πN scattering and the world data of the family of reactions π−p → ηn, K0Λ, K0Σ0, 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.

Inelastic neutrino scattering on 12C and 16O above the particle emission threshold

Recently a new formalism has been developed to described nuclear electromagnetic response within the continuum RPA theory. This model is extended in order to calculate cross sections for weak interactions in nuclei, in particular for inelastic neutrino scattering. The results of a numerical analysis are presented for 12C and 16O. We consider neutrino spectra like those generated in muon decay (relevant for terrestrial experiments) or in a supernova explosion. For the latter case we calculate neutral current cross sections for various neutrino-induced particle reactions on 12C and 16O, relevant for the ν-nucleosynthesis.

Effective quasiparticle G-matrix interaction

Abstract A derivation of the operator structure of the Brueckner G -matrix is presented. This method is used to extract¦an effective interaction based on a G -matrix in nuclear matter derived from a one-boson-exchange potential. Effects of Pauli blocking and short-range correlations have been analyzed, showing that they are essentially restricted to 1 S 0 and 3 S 1 - 3 D 1 states. The reason why the tensor force is not significantly affected by correlations is also discussed. A momentum transfer and density-dependent interaction has been constructed which may be used as a basic ingredient of the full particle-hole interaction to describe the low-lying excited states of nuclei. For further convenience, this interaction has been parametrized in terms of Yukawa-type expressions, which reproduce the exact values within 0.2% in the range of 0–2 fm −1 of momentum transfer. Based on the analysis of an analytical G -matrix, a simple functional form for the density dependence is suggested which provides an excellent fit (within 1%) in the range of the density of 0.35 ϱ 0 ⩽ ϱ ⩽ ϱ 0 . G -matrix interactions based on several phase-shift-equivalent NN potentials are considered in the Landau limit and they show a considerable sensitivity to these potentials. The results can be understood within the context of a very simple model and this provides a better understanding of different channels of the G -matrix interaction, especially those which are relatively poorly understood.

Effects of density dependence of the effective pairing interaction on the first 2+ excitations and quadrupole moments of odd nuclei

Excitation energies and transition probabilities of the first

New results on the limit for the width of the exotic Θ+resonance

2^+

Photocouplings at the pole from pion photoproduction

excitations in even tin and lead isotopes as well as the quadrupole moments of odd neighbors of these isotopes are calculated within the self-consistent Theory of Finite Fermi Systems based on the Energy Density Functional by Fayans et al. The effect of the density dependence of the effective pairing interaction is analyzed in detail by comparing results obtained with volume and surface pairing. The effect is found to be noticeable. For example, the