Kaon photoproduction on the nucleon: Contributions of kaon-hyperon final states to the magnetic moment of the nucleon

By using the Gerasimov-Drell-Hearn (GDH) sum rule and an isobaric model of kaon photoproduction, we calculate contributions of kaon-hyperon final states to the magnetic moment of the proton and the neutron. We find that the contributions are small. The approximation of sigma_{TT'} by sigma_{T} clearly overestimates the value of the GDH integral. We find a smaller upper bound for the contributions of kaon-hyperon final states to the proton's anomalous magnetic moment in kaon photoproduction, and a positive contribution for the square of the neutron's magnetic moment.Comment: 6 pages, revtex, 1 postscript figure, to appear in Phys. Rev.

Electromagnetic Couplings of Nucleon Resonances

An effective Lagrangian calculation of pion photoproduction including all nucleon resonances up to $\sqrt s = 1.7$ GeV is presented. We compare our results to recent calculations and show the influence of different width parametrizations and offshell cutoffs on the photoproduction multipoles. We determine the electromagnetic couplings of the resonances from a new fit to the multipole data.Comment: 20 pages, latex, 6 figures. Misprints corrected, text & 3 figures adde

Exclusive and semi-inclusive strangeness and charm production in πN\pi N and NNNN reactions

Using the Quark-Gluon Strings Model (QGSM) combined with Regge phenomenology we consider the reactions $\pi^- p \to K^0 \Lambda$ and $\pi^- p \to D^- \Lambda_c^+$ which are dominated by the contributions of the $K^*$ and $D^*$ Regge trajectories, respectively. The spin structure of the amplitudes is described by introducing Reggeized Born terms. It is found that the existing data for the reaction $\pi^- p \to K^0 \Lambda$ are in reasonable agreement with the model predictions. To describe the absolute values of the cross sections it is necessary to introduce also suppression factors which can be related to absorption corrections. Furthermore, assuming the SU(4) symmetry to hold for Regge residues and the universality of absorption corrections we calculate the cross section of the reaction $\pi^- p \to D^- \Lambda_c^+$. Employing the latter results from $\pi^- p$ reactions we then estimate the contributions of the pion exchange mechanism to the cross sections of the reactions $NN \to NK\Lambda$ and $NN \to N\bar D \Lambda_c$ and compare them with the contributions of the $K$ and $D$ exchanges. We find that the $NN$ reactions are dominated not by pion exchange but by $K$ and $D$ exchanges, respectively. Moreover, assuming the SU(4) symmetry to hold approximately for the coupling constants $g_{ND \Lambda_c}$ = $g_{NK \Lambda}$ we analyze also the production of leading $\Lambda_c$ hyperons in the reaction $NN \to \Lambda_c X$. It is shown that the non-perturbative mechanism should give an essential contribution to the $\Lambda_c$ yield for $x \geq 0.5$.Comment: 3 pages, LaTeX, 4 postscript figures; contribution to QNP2002, Juelich, June 10-14, 200

Anti-Kaon Induced Reactions on the Nucleon

Using a previously established effective Lagrangian model we describe anti-kaon induced reactions on the nucleon. The dominantly contributing channels in the cm-energy region from threshold up to 1.72 GeV are included (K N, \pi \Sigma, \pi \Lambda). We solve the Bethe-Salpeter equation in an unitary $K$-matrix approximation.Comment: 21 pages, 13 figures, minor typos corrected, accepted for publication in Phys. Rev.

Analysis of resonance multipoles from polarization observables in eta photoproduction

A combined analysis of new eta photoproduction data for total and differential cross sections, target asymmetry and photon asymmetry is presented. Using a few reasonable assumptions we perform the first model-independent analysis of the E0+, E2- and M2- eta photoproduction multipoles. Making use of the well-known A3/2 helicity amplitude of the D13(1520) state we extract its branching ratio to the eta-N channel, Gamma(eta,N)/Gamma = (0.08 +- 0.01)%. At higher energies, we show that the photon asymmetry is extremely sensitive to small multipoles that are excited by photons in the helicity 3/2 state. The new GRAAL photon asymmetry data at higher energy show a clear signal of the F15(1680) excitation which permits extracting an F15(1680)->eta,N branching ratio of (0.15 +0.35 -0.10)%.Comment: 14 pages of LATEX including 7 postscript figure

The ρ\rho Spectral Function in a Relativistic Resonance Model

We calculate the spectral function $A_\rho$ of the $\rho$ meson in nuclear matter. The calculation is performed in the {\it low density} approximation, where the in-medium self energy $\Sigma_{med}$ is completely determined by the vacuum $\rho N$ forward scattering amplitude. This amplitude is derived from a relativistic resonance model. In comparison to previous non-relativistic calculations we find a much weaker momentum dependence of $\Sigma_{med}$, especially in the transverse channel. Special attention is paid to uncertainties in the model. Thus, we compare the impact of different coupling schemes for the $RN\rho$ interaction on the results and discuss various resonance parameter sets.Comment: 47 pages, 19 figures, some discussion and formulae added, minor typos removed, accepted for publication in Nuclear Physics