J. Haidenbauer

Evidence that the a0(980) and f0(980) are not elementary particles

Abstract We study the interesting problem of whether it is possible to distinguish composite from elementary particles. In particular we generalize a model-independent approach of Weinberg to the case of unstable particles. This allows us to apply our formalism to the case of the a 0 (980) and f 0 (980) resonances and to address the question whether these particles are predominantly genuine, confined quark states (of q q or qq q q structure) or governed by mesonic components.

Hyperon-nucleon interactions - a chiral effective field theory approach

We construct the leading order hyperon–nucleon potential in chiral effective field theory. We show that a good description of the available data is possible and discuss briefly further improvements of this scheme

Jülich hyperon-nucleon model revisited

A one-boson-exchange model for the hyperon-nucleon (\Lambda N, \Sigma N) interaction is presented. The model incorporates the standard one boson exchanges of the lowest pseudoscalar and vector meson multiplets with coupling constants fixed by SU(6) flavor symmetry relations. As the main new feature of the model, the contributions in the scalar--isoscalar (\sigma) and vector--isovector (\rho) exchange channels are now constrained by a microscopic model of correlated \pi\pi and K \bar K exchange. Additional short-ranged ingredients of the model in the scalar--isovector (a_0) and scalar--isospin-1/2 (\kappa) channels are likewise viewed as arising from meson-meson correlations but are treated phenomenologically. With this model a satisfactory reproduction of the available hyperon-nucleon data can be achieved.

Hyperon–nucleon interaction at next-to-leading order in chiral effective field theory

Abstract Results for the ΛN and ΣN interactions obtained at next-to-leading order in chiral effective field theory are reported. At the order considered there are contributions from one- and two-pseudoscalar-meson exchange diagrams and from four-baryon contact terms without and with two derivatives. SU(3) flavor symmetry is imposed for constructing the hyperon–nucleon interaction, however, the explicit SU(3) symmetry breaking by the physical masses of the pseudoscalar mesons (π, K, η) and of the involved baryons is taken into account. An excellent description of the hyperon–nucleon system can be achieved at next-to-leading order. It is on the same level of quality as the one obtained by the most advanced phenomenological hyperon–nucleon interaction models.

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.

Pion nucleon scattering in a meson exchange model

The pN interaction is studied within a meson-exchange model and in a coupled-channels approach which includes the channels pN, hN, as well as three effective ppN channels, namely, rN, pD, andsN. Starting out from an earlier model of the Jülich group systematic improvements in the dynamics and in some technical aspects are introduced. With the new model an excellent quantitative reproduction of the pN phase shifts and inelasticity parameters in the energy region up to 1.9 GeV and for total angular momenta Jø3/2 is achieved. Simultaneously, good agreement with data for the total and differential pN→hN transition cross sections is obtained. The connection of the pN dynamics in theS11 partial wave with the reaction pN→hN is discussed.

ETA ' PRODUCTION IN PROTON-PROTON SCATTERING CLOSE TO THRESHOLD

The

Towards a field theoretic understanding of NN → NNπ

pp \to pp \eta^{\prime}

Influence of a Z+(1540) resonance on K+ N scattering

(958) reaction has been measured at COSY using the internal beam and the COSY-11 facility. The total cross sections at the four different excess energies \mbox{

The quark-meson coupling model for Λ, Σ and Ξ hypernuclei

Q = ~1.5 ~MeV, ~1.7 ~MeV, ~2.9 ~MeV,