Quark Baryon Research Articles

ELECTROPRODUCTION OF LIGHT QUARK BARYONS

The status of electromagnetic excitation of light quark (u, d) baryon states is reviewed and confronted with results of calculations within the framework of microscopic models of the baryon structure and the photon — baryon coupling. Prospects for a qualitative improvement of our knowledge in this sector using photon and electron beams at the new, intermediate energy continuous wave (CW) electron machines are discussed.

Light quark baryons

The status of hadronic and electromagnetic excitation of light quark (u, d) baryons states is reviewed and confronted with results of calculations within the framework of microscopic models of the baryon structure and the photon — baryon coupling. Prospects for a qualitative improvement of our knowledge in this sector using photon and electron beams at the new, intermediate energy cw electron machines are discussed.

The Alexander-Zweig (OZI) in multiparticle production. Are there strange quarks in nucleons and pions?

Predictions, theoretical basis, experimental tests and violations of various versions of the AZ (OZI) rule are examined. For bidden production processes for φ and f′ mesons are shown on general grounds to be less suppressed than forbidden decays, without assuming the presence of strange quarks in baryons. Dynamical mechanisms responsible for violations include allowed two-step transitions via intermediate states containinf ordinary hadrons, gluons, flavor-mixed hadrons like η, η′ or f 0(S ∗), and exotic hadrons like glueballs, multiquark states and hybrids. Each case is described by a different mechanism with a different suppression factor.

Color degrees of freedom in a quark-glue plasma at finite baryon density

We derive the color-singlet partition function for a quark-glue plasma with finite quark (baryon number) density by a projection method. Due to colorlessness there is a gradual “freezing” (reduction) of internal degrees of freedom as compared to the Stefan-Boltzmann limit. We find here that this non-perturbative effect is reduced by a finite quark density. A relation between the requirement of colorlessness of all physical states and QCD is proposed.

Instanton effects on the interaction potential between light quarks and the isomultiplet mass splitting of baryons

On the basis of current assumptions of instanton theory we derive strictly the explicit dependence on the masses and spins of the instanton induced potential between a pair of light quarks in baryons, namelyV12=γ+β(m*1+α)(m*2+α)η(1-σ1ησ1), wheremi* andσi(i=1.2) are respectively the mass and Pauli spin of theith quark. On the additional basis of the MIT bag model, we obtain γ=c/R3 and β=b/R3>0, and α>0 is independent of the radiusR of the baryon. The magnitudes of the parametersb and α are also estimated. The MIT bag model is improved by taking into account this potential. Isomultiplet mass splitting formulas are derived in good agreement with experiment.

U 6/2 dynamical supersymmetry in baryons with odd parity

By assigning a odd number of gluons in colour singlet state and a pair ofs1/2 quarks in baryons to the bosonic degree generating the collective effect arising fromL=0 and 2 states, and the fermionic degree tos1/2 quarks, theU6/2 dynamical supersymmetry is applied to the observed mass spectra forN, Δ-, Λ- and Σ-families belonging to the odd parity. A reasonable agreement with the available experimental data is obtained by making use of the group invariants arising from the subgroups ofU6/2.

Some comments on quark masses and baryon magnetic moments

The suggestion made by Lipkin regarding the quark masses and magnetic moments of baryons is examined in the context of the variable pressure bag model. We find that the exact agreement obtained by Lipkin between theory and experiment in the case ofμ(Λ) cannot be considered accidental, contrary to the scepticism expressed by Minami.

QCD enhancement and quenching effect for the magnetic moments of quarks in baryons

QCD enhancement and quenching effect for the magnetic moments of quarks in baryons

On mass corrections and the axial coupling constant in the chiral quark model

We investigate the higher order corrections to the baryon masses and the baryon axial coupling constant g A in a perturbative treatment of the Goldstone pion field. The zeroth-order quark equations of motion in the chiral quark bag model gives the MIT bag results. The next order gives the dominant corrections to the masses and g A . We show that the perturbation expansion of the pion field is justified for large quark bag radii R, but even for R ∼ 1 fm these higher order corrections calculated here are not negligible. A new spacial configuration for the quarks is introduced by the pion tensor force between different up and/or down quarks. The result is that the quarks in baryons have a mixture of S- and D-state wave functions which have important implications on, e.g., g A and the magnetic moments for different baryons as discussed by Glashow. Only baryons with two or more u/d quarks can have D-states. We neglect the tensor forces (and D-states) implied by the gluon exchange between quarks in this discussion.

On the oscillatory modes of quarks in baryons

The color bond structure of a quark-antiquark system is extended, in the long-range approximation, self-consistently to the baryonic three-quark bond structure for SU(3) c and generally to the N-quark bond structure for SU( N) c. The universal ( N-independent) mass square eigenvalues for massless quarks are M 2=(H N) 2≃2m ρ 2 ∑ α=1 3N−3 ν α+ constant, ν α=0,1,2,… .

Baryon spectrum and the forces between quarks

Various forms of the potential between quarks in baryons, including both two-body and three-body forces, are analyzed from a theoretical and phenomenological point of view. We give arguments in favor of a long-range logarithmic potential in baryons playing the analogous role of the linear one in mesons. With this and a short-range Coulomb interaction a good description of the coarse structure of nonstrange baryon resonances emerges. Relativistic corrections can be consistently implemented, leading to an improved picture which only leaves the problem of spin-spin splittings coming out too small.