On equal constituent quark masses in different heavy quarkonia potential models

An Azcarraga-Lukierski supersymmetric particle model, which is invariant with respect to theN=2 extended SuperPoincare group, is quantised by the method of Dirac brackets. The central charges, which satisfy the spin reducing conditions, are conjugate to additional bosonic coordinates in the superspace. The resulting superwavefunction doublet is in one-to-one correspondence with the superfield expansion of Sohnius describing the Fayet hypermultiplet.     

Relativistic constituent quark model and experiments at JLab

Within the relativistic-quantum-mechanics version developed by the present authors in their previous studies, the pion electromagnetic form factor is calculated in the region of high momentum transfers reached and planned to be reached in experiments at the Thomas Jefferson Laboratory (JLab). An asymptotic expansion was obtained for the pion form factor for Q ² → ∞. This expansion describes well existing experimental values and the results of a QCD simulation of future experiments at JLab. It is shown that the region of experiments at JLab is an asymptotic region for the relativistic constituent quark model and that the behavior of the pion form factor, F _π (Q ²)Q ² = const, can be obtained within this model.     

Triply heavy baryons in the constituent quark model

The constituent quark model is used to compute the ground and excited state masses of QQQ baryons containing either c or b quarks.The quark model parameters previously used to describe the properties of charmonium and bottomonium states were used in this analysis.The non-relativistic three-body bound state problem is solved by means of the Gaussian expansion method which provides sufficient accuracy and simplifies the subsequent evaluation of the matrix elements.Several low-lying states with quantum numbers J^P=1/2^±,3/2^±,5/2^±and 7/2^+are reported.We compare the results with those obtained by the other theoretical formalisms.There is a general agreement for the mass of the ground state in each sector of triply heavy baryons.However,the situation is more puzzling for the excited states,and appropriate comments about the most relevant features of our comparison are given.     

Spectroscopy and Regge trajectories of heavy quarkonia in the relativistic quark model

The mass spectra of charmonia and bottomonia are calculated in the framework of the relativistic quark model up to high orbital and radial excitations. The Regge trajectories of heavy quarkonia are constructed both in the (J,M ²) and (n _r ,M ²) planes, where J is the total angular momentum and nr is the radial quantum number. All daughter trajectories turn out to be almost linear and parallel, while parent trajectories exhibit some nonlinearity. Such nonlinearity occurs only in the vicinity of ground states and few lowest excitations and is more pronounced for bottomonia, while it is only marginal for charmonia. The obtained results are compared with available experimental data, and a possible interpretation of the new charmonium-like states above open charm production threshold is discussed.     

Relativistic quark model with quantum chromodynamics, P-states of quarkonia and scalar-vector confinement

In this paper we try to understand several phenomenological issues related to the mass spectra of P-states quarkonia in a relativistic quark model. We give particular emphasis on understanding the most recent experimental data within a relativized scalar-vector confining potential. In this paper we extend the previous works on the studies of quark confinement in non-relativistic QCD, using a formalism which uses a covariant Hamiltonian in the centre of mass frame. The spin-structure of the potential is obtained from the reduction of Bethe-Salpeter equation into Breit-interaction. Printed as S Chakrabarty in several papers published earlier e.g. References [1,11] etc. of this paper.     

Relativistic effects in quarkonia decays with axion production

In the framework of the potential approach it is shown that relativistic effects connected with the relative motion of quarks in quarkonia lead to a strong decrease in the values of the ratios Br(ψ→aγ)/Br(ψ→μ⁺μ⁻) and B Br(ϒ→aγ)/Br(ϒ→μ⁺μ⁻), predicted by the nonrelativistic quark model. This does not allow to exclude already unambiguously the existence of a long-lived axion on the basis of available experimental data on these decays.     

Recent experimental data and the size of the quark in the constituent quark model

We use the constituent quark model (CQM) to describe CDF data on double parton cross section and HERA data on the ratio cross section of elastic and inelastic diffractive productions. Our estimate shows that the radius of the constituent quark turns out to be rather small, GeV^-2, in accordance with the assumption on which CQM is based. Received: 14 April 2002 / Published online: 9 August 2002     

Photoproduction of pions in the constituent quark model

Threshold photoproduction of pions has been calculated for composite systems, both for the nucleon in terms of constituent quarks and the ³H/³He isodoublet in terms of nucleons. The results of the low energy theorems are recovered only if both size effects and internal excitation of the composite system are properly taken into account. In particular, the ground state has to be non-degenerate and the excitation spectrum has to have the proper symmetries of the many-body system.     

The Drell-Hearn-Gerasimov sum rule and the constituent quark model

The helicity structure function of the nucleon has been calculated for the constituent quark model and compared to the prediction of the Drell-Hearn-Gerasimov sum rule. The multipole decomposition of the sum rule shows large cancellations between different resonances. The small isoscalar-isovector contribution is related to the admixture of aD-state (bag deformation) in the nucleon's wave function. The calculations indicate a relatively slow saturation of this part of the sum rule with excitation energy.Work supported by Deutsche Forschungsgemeinschaft and Istituto Nazionale di Fisica Nucleare