Narrow Results

Studying the Bethe–Salpeter formalism for interactions instantaneous in the rest-frame of the bound states described, we show that, for bound-state constituents of arbitrary masses, the mass of the ground state of a given spin may be calculated almost entirely analytically with high accuracy, without the (numerical) diagonalization of the matrix representation obtained by expansion of the solutions over a suitable set of basis states.

In this report, the theoretical framework of the chiral SU(3) quark model is introduced briefly. By using this model the NN, YN and KN scattering processes, the structures of dibaryon states and pentaquark states are studied. A new interesting dibaryon candidate (ΩΩ)_0⁺ is predicted.

The S, P, D, F wave KN phase shifts have been studied in the chiral SU(3) quark model by solving a resonating group method equation. The numerical results of different partial waves are in agreement with the experimental data except for the cases of P₁₃ and D₁₅, which are less well described when the laboratory momentum of the kaon meson is greater than 400 MeV.

We give the comparisons between the chiral SU(3) quark model and the extended chiral SU(3) quark model. The results show that the phase shifts of NN scattering are very similar. However, the short range mechanisms of nucleon-nucleon interaction are totally different. In the chiral SU(3) quark model, the short range interaction is dominantly from OGE, and in the extended chiral SU(3) quark model, it is dominantly from vector meson exchanges.

In my talk I discussed the properties of the newly discovered , D_sJ(2460), X(3872), and SELEX states and suggested experimental measurements that can shed light on them. In this writeup I concentrate on an important facet of under-standing the D_sJ states, the properties of the closely related and D′₁ states. These states are well described as the broad, j = 1/2 non-strange charmed P-wave mesons.

A quark model is applied to the spectrum of baryons containing heavy quarks. The model gives masses for the known heavy baryons that are in agreement with experiment, but for the doubly-charmed baryon Ξ_cc, the model prediction is too heavy. Mixing between the Ξ_Q and Ξ′_Q states is examined and is found to be small for the lowest lying states. In contrast with this, mixing between the Ξ_bc and Ξ′_bc states is found to be large, and the implication of this mixing for properties of these states is briefly discussed. We also examine heavy-quark spin-symmetry multiplets, and find that many states in the model can be placed in such multiplets. We compare our predictions with those of a number of other authors.

The hybrid meson is one of the most interesting new hadron species beyond the naive quark model. It acquire great attention both from the theoretical and experimental efforts. Many good candidates have been claimed to be observed, but there is no absolute confirmation about the existence of hybrid mesons. In the present work we propose new calculations of the masses and decay widths of the hybrid mesons in the context of constituent gluon model.

The semileptonic decays of the lowest-lying double-heavy baryons are treated in a quark model. For the Ξ_bb, hyperfine mixing in the spin wave function leaves the total rate for decay into the lowest lying daughter baryons essentially unchanged, but changes the relative rates into the Ξ_bc and . The same pattern is obtained in the decays of the Ω_bb. For the Ξ_bc, this mixing leads to factor of about 17 suppression in the decay rate to the when wave functions truncated to the largest components are used, but the total semileptonic decay rate of the parent baryon remains essentially unchanged. For the Ω_bc, the decay to the is suppressed by a factor of more than 25 from the unmixed case. When the full wave functions are used, the large suppression of the decays to the and persists.

On the basis of the phenomenological relativistic harmonic models for quarks, we have obtained the masses of P-wave mesons. The full Hamiltonian used in the investigation has Lorentz scalar + vector confinement potential, along with one-gluon-exchange potential (OGEP) and the instanton-induced quark–antiquark interaction (III). A good agreement is obtained with the experimental masses. The respective role of III and OGEP for the determination of the meson masses is discussed.

Supposing quark–diquark structure of baryons, we look for systematics of baryons composed of light quarks (q = u, d). We systematize baryons using the notion of two diquarks: (i) axial–vector state, , with the spin S_D = 1 and isospin I_D = 1 and (ii) scalar one, , with the spin S_D = 0 and isospin I_D = 0. We consider several schemes for the composed baryons: (1) with different diquark masses, , (2) with and overlapping and states (resonances), (3) with/without SU(6) constraints for low-lying states (with quark–diquark orbital momenta L = 0). In the high-mass region, the model predicts several baryon resonances at M ~ 2.0–2.9 GeV. Moreover, the model gives us the double pole structure (i.e. two poles with the same Re M but different Im M) in many amplitudes at masses M ≳ 2.0 GeV. We see also that for description of low-lying baryons (with L = 0), the SU(6) constraint is needed.

We continue our attempts to systematize baryons, which are composed of light quarks (q = u, d), as quark–diquark systems. The notion of two diquarks is used: (i) , with the spin S_D = 1 and isospin I_D = 1 and (ii) , with S_D = 0 and I_D = 0. Here we try to resolve the problem of the low-lying states: in the last experiments the lightest state is observed at ≳2200 MeV, not at 1900–2000 MeV as it has been stated 20 years ago. We are looking for different systematization variants with the forbidden low-lying states in the mass region ≲2000 MeV. We see that the inclusion of the SU(6) constraints on states with angular momentum L = 1 results in a shift of the lightest isobar to ~2300 MeV. The scheme with the SU(6) constraints for low-lying and states (with L = 0, 1) is presented in detail.

We present new results concerning the masses and the decay widths of the most interesting hybrid meson states taking as inputs the gluon mass m_g and the nonperturbative QCD running coupling constant α_s(0) coming from both LQCD and SDE recent estimations.

Hadronic form factors for the rare weak transitions Λ_b → Λ^(*) are calculated using a nonrelativistic quark model. The form factors are extracted in two ways. An analytic extraction using single-component wave functions (SCA) with the quark current being reduced to its nonrelativistic Pauli form is employed in the first method. In the second method, the form factors are extracted numerically using the full quark model wave function (MCN) with the full relativistic form of the quark current. Although there are differences between the two sets of form factors, both sets satisfy the relationships expected from the heavy quark effective theory (HQET). Differential decay rates, branching ratios (BRs) and forward–backward asymmetries (FBAs) are calculated for the dileptonic decays Λ_b → Λ^(*) ℓ⁺ ℓ^-, for transitions to both ground state and excited daughter baryons. Inclusion of the long distance contributions from charmonium resonances significantly enhances the decay rates. In the MCN model the Λ(1600) mode is the dominant mode in the μ channel when charmonium resonances are considered; the Λ(1520) mode is also found to have a comparable BR to that of the ground state in the μ channel.

We perform a systematic study of the bound state problem of and systems by using effective interaction in our chiral quark model. Our results show that both the interactions of and states are attractive, which consequently result in and bound states.

After a short review of the activities of Shoichi Sakata and his group, how the six-quark model explains CP violation is described. Experimental verification of the model at the B-factories is also briefly discussed.

In this paper, we survey the radial and orbital excitations of I = 0 and systems anticipated up to 2.0 GeV in the framework of the chiral quark model. The Schrödinger equation is solved by using Gaussian expansion method. And using the wave functions obtained, instead of the simple harmonic oscillator wave functions, we study systematically the two-body strong decay (limited to S + S modes) of the systems. By comparing with the experimental data, we try to identify the normal states and exotic states.

Branching ratios, lepton forward–backward asymmetries, and lepton polarization asymmetries for the flavor-changing neutral current (FCNC) dileptonic decays of the ${\Lambda }_b$ baryon to the ground state and a number of excited state $\Lambda$ baryons are calculated using form factors extracted using wave functions from a constituent quark model. The SM branching ratios for the transition to the ground state calculated using these quark model form factors are consistent with the recent measurement reported by the LHCb collaboration. It is shown that the lepton polarization asymmetries are largely insensitive to the transition form factors and, therefore, may also be insensitive to the effects of QCD in the nonperturbative regime. These observables could therefore provide somewhat model independent ways of extracting various combinations of the Wilson coefficients.

Exotic mesons with hidden strange $(s\bar{s})$ and heavy quark pairs $(Q\bar{Q})$, where $Q=c$, $b$, are considered as diquark–antidiquark systems, $(Qs)\cdot (\bar{Q}\bar{s})$. Taking into account that these states can recombinate into two-meson ones, we study the interplay of these states in terms of the dispersion relation $D$-function technique. The classification of exotic mesons is discussed, coefficients for decay modes are given, predictions for new states are presented. The nonet structure for $(Qq)\cdot (\bar{Q}\bar{q})$, $(Qs)\cdot (\bar{Q}\bar{s})$, $(Qq)\cdot (\bar{Q}\bar{s})$-states $(q=u,d)$ is suggested.

Nonstrange and strange pentaquarks with hidden charm are considered as diquark–diquark–antiquark composite systems. Spin and isospin content of such exotic states is discussed and masses are evaluated.

Hadronic resonance propagators which take into account the analytical properties of decay processes are built in terms of the dispersion relation technique. Such propagators can describe multi-component systems, for example, those when quark degrees of freedom create a resonance state, and decay products correct the corresponding pole by adding hadronic deuteron-like components. Meson and baryon states are considered, examples of particles with different spins are presented.