Quark model recent issues.pdf

a r X i v : 0 7 1 0 .2 0 4 6 v 1 [ h e p - p h ] 1 0 O c t 2 0 0 7 Quark model: recent issues on Meson-Nucleon Physics and the Structure of the Nucleon September10-14, 2007 IKP, Forschungzentrum Jülich, Germany Fl. Stancu Institute of Physics, B.5 University of Lie?ge Sart Tilman, B-4000 Lie?ge 1 Belgium Abstract In the first part I briefly survey recent issues in constituent quark models raised by the observation of unusual hadronic states. In particular I dis- cuss the role of higher Fock components in the wave function of baryons and the possible interpretation of open charm and of new charmonium-type resonances as tetraquarks. In the second part I show support for the quark model dynamics obtained in a model independent way from the 1/Nc expan- sion approach of QCD which proved to be successful in describing baryon properties. 1 Introduction The organizers asked me to talk about recent issues in the quark model (QM). This is a vast subject and I had to make a selective choice. My talk contains two distinctive parts. The first is devoted to specific issues in the QM related to the recent observation (since 2003) of unusual hadronic states. In this context I present a few aspects of the QM developments in the light of the newly found resonances. The second part is devoted to a comparison between QM results and the 1/Nc expansion approach of QCD, both being successful in baryon spectroscopy, the latter being closer to QCD and model independent. 2 The QM and the newly found resonances Here I refer to constituent quark (or potential) models. The basic assump- tions are that the Hamiltonian consists of a kinetic (non-relativistic or rela- tivistic) part, a confinement part and a hyperfine interaction of a one-gluon 1 Fl. Stancu Quark model: recent issues exchange (OGE) type, a Goldstone boson exchange (GBE) type or resulting from an instanton induced interaction (III), or a mixture of them. The quark models are generally successful in reproducing baryon spectr