L. R. Dai ( Department of Physics, Liaoning Normal University) Z.Y. Zhang, Y.W. Yu

1. L. R. Dai (Department of Physics, Liaoning Normal University) Z.Y. Zhang, Y.W. Yu (Institute of High Energy Physics, Beijing, China)

2. Outline Ⅰ:Motivations • The chiral SU(3) quark model ‘s success • baryon structure’s study on quark level • the successful study on nucleon level Ⅱ:The Model • The extended chiral SU(3) quark model • Determination of parameters Ⅲ: Result and discussion Ⅳ: Summary

3. Ⅰ:Motivations The chiral SU(3) quark model (Nucl.Phys. 625(1997)59) In this model,the coupling between chiral field and quark is introducedto describe low momentum medium range NPQCD effect.The interacting Lagrangian can be written as: . scalar nonet fields pseudo-scalar nonet fields It is easy to prove that is invariant under the infinitesimal chiral transformation. This can be regarded asan extension of the SU(2) - σ model for studying the system with s quark.

4. In chiral SU(3) quark model, we still employ an effective OGE interaction to govern the short range behavior, and a confinement potential to provide the NPQCD effect in the long distance. Hamiltonian of the system: ( is taken as quadratic form.)

5. 1: long range => confinement2: short range =>OGE –color dependent

6. spin-flavor dependent The expressions of and : Here we have only one coupling constant,

7. In this chiral SU(3) quark model, in which short range repulsion is described by OGE Using the same set of parameters • Energies of the baryon ground state • NN scattering phase shifts • Hyperon-nucleon (YN) cross sections can be reproduced reasonably. * The detailed results have been presented by Prof.Zhang’s talk today morning!

8. sincelast few years, shen et al, Riska andGlozman applied the quark-chiral field coupling model to study the baryon structure. Phys. Rev. C55(1997) Phys.Rep.268(1996)263; Nucl.Phys.A663(2000) They have found : The chiral field coupling is important in explaining the structures of baryons.

9. As is well known,on baryon level, the short range repulsion is described successfully by vector meson (ρ,ω, K* and φ) exchanges. Naturally, we would like to ask which is the right mechanism for describing the short range interactions ? 1: OGE 2: vector meson exchange 3: or both of them are important

10. with vector meson exchange on quark level no dynamical calculations before !!

11. Ⅱ:The ModelThe Extended chiral su(3) quark Model Based on the chiral SU(3) quark model, we further add vector effective Lagrangian gchv :Vector coupling constant fchv: Tensor coupling constant The Hamiltonian of the system

12. new => “extend” 1: quark-vector fileld coupling 2:spin-flavor dependent color – independent

13. Parameters: (1). Input part: taken to be the usual values. (2). Chiral field part: is adjustable. and are taken to be experimental values, cutoff mass: Λ=1100 Mev, chiral symmetry breaking scale

14. (3). OGE and confinement part: and are fixed by and . is determined by the stability condition of Modelparameters and the corresponding binding nergies of deuteron

15. Modelparameters and the corresponding binding nergies of deuteron

16. Ⅲ: RESULTS To study two baryon system, we did a two-cluster dynamical RGM calculation Phase shifts of N-N scattering S wave with 3 sets of parameters single channel

17. N-N P-wave scattering

18. N-N D-wave scattering

19. N-N F-wave scattering

20. *About NΔeffect Discuss: NN 1S0 scattering . Extended Model with setI (fchv/gchv =0) Extended Model with setII (fchv/gchv =2/3) red line : with NΔ coupling black line : without NΔ coupling

21. To get reasonable 1S0 phase shifts

22. * 3S1-wave scattering 1: for different models almost the same good agreement with exp. 2: bu from 0.5 (not extended) to 0.45fm (extended model) Means the bare radius of baryon becomes smaller when more meson clouds are included.

23. *Mechanisms for short range interactionare totally different 1: When the vector meson field coupling is considered, the coupling constant of OGE is largely reduced by fitting the mass difference between Δ and N. 2: in the extended chiral SU(3) quark model, instead of the OGE, the vector meson exchanges play an important role for the short range interaction between two quarks

24. GCM ( generator coordinating method ) potential chira su(3) quark model Extended su(3) quark model with setII in Extended Model1: OGE is weak2:The vector meson exchange is dominate!

25. *Diagonal matrix elementsofgenerator coordinating method (GCM) for π, ρ andω mesons One can see that the ω meson exchange offers repulsion not only in the short range region, but also in medium range part. This property is different from that of π meson, which only contributes repulsive core.

26. * the coupling constants of the vector meson exchange gchv and fchv on quark level: set I: fchv/gchv=0 , gchv =2.35 fchv =0 set II: fchv/gchv=2/3 , gchv =1.97 fchv =1.32 on nucleon level gωNN ≈10-15 forω meson , gρNN ≈2-3 forρ meson Nijmegen model D gρNN ≈2.09 and fρNN =17.122 The coupling constantis muchweakeron quark levelthan on baryon level. becauseon quark level ① the size effect b ②the quark exchanges between two nucleon clusters both contribute short range repulsion

27. Ⅳ:summary 1: The vector meson (ρ,ω) exchange effect in N-N scattering processes on quark level is studied in the extended chiral SU(3) quark model. 2: The phase shifts of 1S0 and 3S1 waves can be fitted rather well. 3:the strength of OGE interaction is greatly reduced and the short range NN repulsion is due to vector meson exchanges (instead of OGE), which also results in smaller size parameter bu.