Quark model: recent issues

In the first part I briefly survey recent issues in constituent quark models raised by the observation of unusual hadronic states. In particular I discuss 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 $1/N_c$ expansion approach of QCD which proved to be successful in describing baryon properties.Comment: 10 pages, invited talk at MENU2007, September 10-14, 2007, Juelich, German

Jazz in British new wave cinema - An interview with Sir John Dankworth

Sir John Dankworth, the eminent English composer, conductor, bandleader and jazz musician has written in many genres, including composing over 20 film scores. Of these, Saturday Night and Sunday Morning (1960), The Criminal (1960), The Servant (1963) and Darling (1965) in particular, played a major role in bringing about a new sound in British film during the 1960s. This interview explores Sir John Dankworth's contribution to this innovative Film genre through his jazz-influenced musical scores

Positive parity pentaquarks in a Goldstone boson exchange model

We study the stability of the pentaquarks uuddQbar, uudsQbar and udssQbar (Q = c, b, or t) of positive parity in a constituent quark model based on Goldstone boson exchange interaction between quarks. The pentaquark parity is the antiquark parity times that of a quark excited to a p-shell. We show that the Goldstone boson exchange interaction favors these pentaquarks much more than the negative parity ones of the same flavour content but all quarks in the ground state. We find that the nonstrange pentaquarks are stable against strong decays.Comment: 13 pages, RevTe

Multiquark states in a Goldstone boson exchange model

We discuss the stability of multiquark systems containing heavy flavours. We show that the Goldstone boson exchange (GBE) model gives results at variance with the one-gluon-exchange (OGE) model, i.e. when the GBE model stabilizes a system the OGE model destabilizes it and vice-versa.Comment: 7 pages, RevTeX, Talk given at Joint ECT*/TJNAF workshop on N* physics and non-perturbative QCD, May 18-29, 1998, ECT*, Trento, Italy, to be published in Few-Body Systems Supp

Stability of pentaquarks with a two- plus three-body chromoelectric interaction

We study the stability of pentaquarks within a schematic model based on SU(3) color symmetry, by taking into account algebraic arguments leading to a chromoelectric interaction containing two- and three-body parts. It has already been proven that such an interaction can influence the spectrum of ordinary baryons and the stability of tetraquarks and hexaquarks.Comment: 11 pages, 1 figure, it matches the published versio

Exploring the spectrum of the hidden charm strange pentaquark in an SU(4) flavor-spin model

We study the spectrum of the isoscalar pentaquark $udsc\overline{c}$, of either positive or negative parity, in a constituent quark model with linear confinement and a flavor-spin hyperfine interaction previously extended to SU(4) and used to describe the spectrum of the $uudc\overline{c}$ pentaquarks observed at LHCb in 2019. For positive parity we make a distinction between the case where one unit of angular momentum is located in the subsystem of four quarks and the case where the angular momentum is located in the relative motion between a ground state four-quark subsystem and the antiquark. The novelty is that we introduce the coupling between different flavor states, due to the breaking of exact SU(4)-flavor symmetry of the Hamiltonian model, both for positive and negative parity states. An important consequence is that the lowest state, located at 4404 MeV, has quantum numbers $J^P$ = $1/2^-$ while without coupling the lowest state has $J^P$ = $1/2^+$ or $3/2^+$.Comment: 26 pages, title slightly changed, other minor changes, it matches the published version. arXiv admin note: text overlap with arXiv:1902.0710

Dynamics of pentaquarks in constituent quark models: recent developments

Some recent developments in the study of light and heavy pentaquarks are reviewed, mainly within constituent quark models. Emphasis is made on results obtained in the flavor-spin model where a nearly ideal octet-antidecuplet mixing is obtained. The charmed antisextet is reviewed in the context of an SU(4) classification.Comment: Based on talks given at the "Workshop Three days of Hadronic Physics", Joint Meeting Heidelberg-Liege-Paris-Rostock, December 16-18, 2004, Spa, Belgium and the International Workshop "Exotic Hadrons", February 21-24, 2005, ECT* Trento, Italy, 9 pages, 1 figure, submitted to AIP Conf. Pro

Structure of light and heavy pentaquarks

Light and heavy pentaquarks are described within a constituent quark model based on a spin-flavor hyperfine interaction. In this model the lowest state acquires positive parity. The masses of the light antidecuplet members are calculated dynamically using a variational method. It is shown that the octet and antidecuplet states with the same quantum numbers mix ideally due to SU(3)$_F$ breaking. Masses of the charmed antisextet pentaquarks are predicted within the same model.Comment: 6 pages, 2 figures, Plenary talk at the 10th International Symposium on Meson-Nucleon Physics and the Structure of the Nucleon (MENU04), Beijing, August 29 - September 4, 2004, reference adde

X(5568) as a sudˉbˉs u \bar d \bar b tetraquark in a simple quark model

The $S$-wave eigenstates of tetraquarks of type $s u \bar d \bar b$ with J$^{P}$ = 0$^{+}$, 1$^{+}$ and 2$^{+}$ are studied within a simple quark model with chromomagnetic interaction and effective quark masses extracted from meson and baryon spectra. It is tempting to see if this spectrum can accommodate the new narrow structure X(5568), observed by the D\O~~Collaboration, but not confirmed by the LHCb Collaboration. If it exists, such a tetraquark is a system with four different flavors and its study can improve our understanding of multiquark systems. The presently calculated mass of X(5568) agrees quite well with the experimental value of he D\O~~Collaboration. Predictions are made for the spectrum of the charmed partner $s u \bar d \bar c$. However we are aware of the difficulty of extracting effective quark masses, from mesons and baryons, to be used in multiquark systems.Comment: 18 pages, 3 figures, it matches the published version in J.Phys.G43,105001. arXiv admin note: text overlap with arXiv:0906.248