Magnetic dipole,electric quadrupole and magnetic octupole moments of the <Emphasis Type="Italic">Δ</Emphasis> baryons in light cone QCD sum rules

Due to the very short life time of the Δ baryons, a direct measurement on the electromagnetic moments of these systems is almost impossible in the experiment and can only be done indirectly. Although only for the magnetic dipole moments of Δ ⁺⁺ and Δ ⁺ systems there are some experimental data, the theoretical, phenomenological and lattice calculations could play crucial role. In the present work, the magnetic dipole (μ _Δ ), electric quadrupole (Q _Δ ) and magnetic octupole (O _Δ ) moments of these baryons are computed within the light cone QCD sum rules. The results are compared with the predictions of the other phenomenological approaches, lattice QCD and existing experimental data.     

Magnetic moments of decuplet baryons in an independent particle potential model

Magnetic moments of decuplet baryons have been calculated in a relativistic independent quark model with a phenomenological potential in equally mixed scalar-vector harmonic form. Such a model has been successful in describing wide ranging hadronic phenomena in mesonic and baryonic sectors. Using the solutions of the constituent quark orbitals with the model parameters taken from its earlier applications, the magnetic moments of decuplet baryons Δ⁺⁺ and Ω⁻ have been obtained which are in good agreement with the available experimental data. However, the agreement is found to be much better when the magnetic moment ratios such as μ_δ++/μ _p and μ_Ω-/μ_Λ are considered. Model predictions for the magnetic moments of other decuplet baryons together with the charge radii have also been calculated which may be verified in future experiments.     

Baryon octupole moments<Superscript>⋆</Superscript>

We report on a calculation of higher electromagnetic multipole moments of baryons in a non-covariant quark model approach. The employed method is based on the underlying spin-flavor symmetry of the strong interaction and its breaking. We present results on magnetic octupole moments of decuplet baryons and discuss their implications.     

Quark-diquark approximation of the three-quark structure of baryons in the quark confinement model

Octet (1/2⁺) and decuplet (3/2⁺) baryons as relativistic three-quark states are investigated using the quark confinement model (QCM), the relativistic quark model, based on some assumptions about hadronization and quark confinement. The quark-diquark approximation of the three-quark, structure of baryons is proposed. In the framework of this approach, the main low-energy characteristics of baryons, such as magnetic moments, electromagnetic radii and form factors, the ratio of axial and vector constants in semileptonic baryon decays, strong form factors and decay widths, are described. The obtained results agree with experimental data.     

Static properties and semileptonic decays of doubly heavy baryons in a nonrelativistic quark model

We evaluate static properties and semileptonic decays for the ground state of doubly heavy Ξ, Ξ', Ξ ^* and Ω, Ω', Ω ^* baryons. Working in the framework of a nonrelativistic quark model, we solve the three-body problem by means of a variational ansatz made possible by heavy-quark spin symmetry constraints. To check the dependence of our results on the inter-quark interaction we use five different quark-quark potentials that include a confining term plus Coulomb and hyperfine terms coming from one-gluon exchange. Our results for static properties (masses, charge radii and magnetic moments) are, with a few exceptions for the magnetic moments, in good agreement with a previous Faddeev calculation. Our much simpler wave functions are used to evaluate semileptonic decays of doubly heavy Ξ, Ξ'(J = 1/2) and Ω, Ω'(J = 1/2) baryons. Our results for the decay widths are in good agreement with calculations done within a relativistic quark model in the quark-diquark approximation. An erratum to this article is available at .     

Meson-baryon s-wave resonances with strangeness -3

Starting from a consistent SU(6) extension of the Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian ( Phys. Rev. D 74, 034025 (2006)), we study the s-wave meson-baryon resonances in the strangeness S = - 3 and negative-parity sectors. Those resonances are generated by solving the Bethe-Salpeter equation with the WT interaction used as kernel. The considered mesons are those of the 35-SU(6)-plet, which includes the pseudoscalar (PS) octet of pions and the vector (V) nonet of the rho-meson. For baryons we consider the 56-SU(6)-plet, made of the 1/2⁺ octet of the nucleon and the 3/2⁺ decuplet of the Delta. Quantum numbers I(J ^P) = 0(3/2^-) are suggested for the experimental resonances Ω ^*(2250)^- and Ω ^*(2380)^-. Among other, resonances with I = 1 are found, which minimal quark content is sssˉl', being s the strange quark and l, l' any of the the light up or down quarks. A clear signal for such a pentaquark would be a baryonic resonance with strangeness -3 and electric charge -2 or 0, in proton charge units. We suggest looking for K ^- Ξ ^- resonances with masses around 2100 and 2240MeV in the sector 1(1/2^-), and for π ^± Ω ^- and K ^- Ξ ^*- resonances with masses around 2260MeV in the sector 1(3/2^-).     

Transition magnetic moments of J~P=3/2~+ decuplet to J~P=1/2~+ octet baryons in the chiral constituent quark model

In light of the developments of the chiral constituent quark model(χ~(CQM)) in studying low energy hadronic matrix elements of the ground-state baryons, we extend this model to investigate their transition properties.The magnetic moments of transitions from the J~P=3/2~+ decuplet to J~P=1/2~+ octet baryons are calculated with explicit valence quark spin, sea quark spin and sea quark orbital angular momentum contributions. Since the experimental data is available for only a few transitions, we compare our results with the results of other available models. The implications of other complicated effects such as chiral symmetry breaking and SU(3) symmetry breaking arising due to confinement of quarks are also discussed.     

Charge radii of octet and decuplet baryons in chiral constituent quark model

The charge radii of the spin- $\frac{1}{2}^+$ octet and spin- $\frac{3}{2}^+$ decuplet baryons have been calculated in the framework of chiral constituent quark model (χCQM) using a general parametrization method (GPM). Our results are not only comparable with the latest experimental studies but also agree with other phenomenological models. The effects of SU(3) symmetry breaking pertaining to the strangeness contribution and GPM parameters pertaining to the one-, two- and three-quark contributions have also been investigated in detail and are found to be the key parameters in understanding the non-zero values for the neutral octet (n, Σ⁰, Ξ⁰, Λ) and decuplet (Δ⁰, Σ^*0, Ξ^*0) baryons.     

Magnetic moments of (JP = 3/2+) heavy baryons using effective mass and screened charge scheme

Magnetic moments of heavy charmed baryons with J ^P = 3/2⁺ are predicted employing the concept of effective quark mass and screened charge of quark. We also extend our scheme to predict the 3/2⁺ ? \rightarrow 1/2⁺ transition magnetic moments. A comparison of our results with the predictions obtained in recent models is presented.     

Photoproduction of pairs of neutral fermions with a magnetic moment in the field of a nucleus of arbitrary spin

We have investigated the electromagnetic (Bethe-Heitler) process of the formation of a pair of neutral baryons of spin 1/2 by a photon in the field of a nucleus possessing electric quadrupole and magnetic dipole and octupole moments. The cross section for photoproduction of neutron-antineutron pairs has been found as a function of the electric (Ze, Q) and magnetic (_I, ) multipole moments of the target nucleus. The angular distribution and energy spectrum of the neutron of the pair produced have been studied for⁹Be,¹²C, and⁴⁰Ca nuclei.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 69–75, May, 1982.     

Signatures of chiral dynamics in the nucleon to Delta transition⋆

Utilizing the methods of chiral effective field theory we present an analysis of the electromagnetic NΔ-transition current in the framework of the non-relativistic “small scale expansion” (SSE) to leading-one-loop order. We discuss the momentum dependence of the magnetic dipole, electric quadrupole and Coulomb quadrupole transition form factors up to a momentum transfer of Q² < 0.3GeV^2. Particular emphasis is put on the identification of the role of chiral dynamics in this transition. Our analysis indicates that there is indeed non-trivial momentum dependence in the two quadrupole form factors at small Q² < 0.15GeV^2 arising from long-distance pion physics, leading, for example, to negative radii in the (real part of the) quadrupole transition form factors. We compare our results with the EMR(Q²) and CMR(Q²) multipole ratios from pion-electroproduction experiments and find a remarkable agreement up to four-momentum transfer of Q² ≈ 0.3GeV^2. Finally, we discuss the chiral extrapolation of the three transition form factors at Q² = 0, identifying rapid changes in the (real part of the) quark mass dependence of the quadrupole transition moments for pion masses below 200MeV, which arise again from long-distance pion dynamics. Our findings indicate that dipole extrapolation methods currently used in lattice QCD analyses of baryon form factors are not applicable for the chiral extrapolation of NΔ quadrupole transition form factors.     

Excited states of confined quarks

Low lying excitations of colored quarks and gluons are studied in the bag theory. The baryons and mesons considered have one quark in a P-wave excited state and the remainder in the ground state. They correspond to 1/2⁻ and 3/2⁻ baryons and to 0⁺ and 1⁺ mesons. Gluon hyperfine interactions are included to lowest order. SU(3) is broken by the strange quark mass. All parameters of the model were determined previously by fitting the masses of the light hadrons. The calculated masses of these states are generally found to be lighter than the observed states. Our spectrum contains states which do not occur in models of quark confinement with only two body forces but which should be present in the physical spectrum of any baglike confinement model.     

Electromagnetic Structure of the �� Baryon within the Covariant Spectator Theory

We calculated all the electromagnetic observables for the nucleon and its lowest-lying ??(1232) excitation within a constituent quark model for those two baryons based on the covariant spectator theory. Once the reactions ?? N ?? N and ?? N ?? ?? were described, we predicted without further adjusting of parameters the four electromagnetic ?? form factors: the electric charge G _E0, the magnetic dipole G _M1, the electric quadrupole G _E2 and the magnetic octupole G _M3. The results are compatible with the available experimental data and recent lattice QCD data.     

Magnetic moments and structure of the nuclei3H,3He and of baryons

From a solution of the problem of magnetic moments of the nuclei³H and³He, two properties are obtained: - These nuclei have mixed orbital ground states. - These states are not charge symmetric. The first property is expected to hold also for baryons in the quark model, on account of recently measured magnetic moments. Supporting evidence and implications for baryon structure are discussed.     

Strong decays Σ*→Σπ,Λπ and related strong coupling constant

We calculate the strong coupling constant g among the decuplet baryons, the octet baryons and the pseudoscalar mesons in the heavy baryon chiral perturbation theory with the light-cone QCD sum rules, and we study the strong decays Σ ^*→Λ π,Σ π. The numerical value of the strong coupling constant g is consistent with our previous calculation; the central values lead to small SU(3) breaking effects, less than 6%; and no definitive conclusion can be drawn due to the large uncertainties.     

On the nature of the lowest 1/2<Superscript>-</Superscript> baryon nonet and decuplet<Superscript>⋆</Superscript>

From our recent study of properties of the lowest spin-parity 1/2^- baryons, N ^*(1535) and Δ^*(1620) , new pictures for the internal structure of the lowest 1/2^- baryon nonet and decuplet are proposed. While the lowest 1/2^- baryon nonet may have large diquark-diquark-antiquark component, the lowest 1/2^- baryon decuplet is proposed to have large vector-meson-baryon components. Evidence for “missing" members of the new pictures is pointed out and suggestions are made for detecting these predicted states from forthcoming experiments.