Radial excitations of low–lying baryons and the Z + penta–quark

Abstact: Within an extended Skyrme soliton model for baryons the interplay between the collective radial motion and the SU(3)–flavor–rotations is investigated. The coupling between these modes is mediated by flavor symmetry breaking. Collective coordinates which describe the corresponding large amplitude fluctuations are introduced and treated canonically. When diagonalizing the resulting Hamiltonian flavor symmetry breaking is fully taken into consideration. As eigenstates not only the low–lying (1/2)⁺ and (3/2)⁺ baryons but also their radial excitations are obtained and compared to the empirical data. In particular the relevance of radial excitations for the penta–quark baryon Z ⁺ (Y=2, I=0, J ^π=(1/2)⁺) is discussed. In this approach its mass is predicted to be 1.58 GeV. Furthermore the widths for various hadronic decays are estimated which, for example, yields Γ(Z ⁺→NK) ∼ 100 MeV for the only permissible decay process of the Z ⁺. Received: 20 April 1998 / Revised version: 29 May 1998     

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.     

Structure and reactions of pentaquark baryons

We review the current status of the exotic pentaquark baryons. After a brief look at experiments of both positive and negative results, we discuss theoretical methods to study the structure and reactions for the pentaquarks. First we introduce the quark model and the chiral soliton model, where we discuss the relation of mass spectrum and parity with some emphasis on the role of chiral symmetry. It is always useful to picture the structure of the pentaquarks in terms of quarks. As for other methods, we discuss a model-independent method, and briefly mention the results from the lattice and QCD sum rule. Decay properties are then studied in some detail, which is one of the important properties of ⊝⁺. We investigate the relation between the decay width and the quark structure having certain spin-parity quantum numbers. Through these analyses, we consider as plausible quantum numbers of ⊝⁺,J ^P = 3/2⁻. In the last part of this note, we discuss production reactions of ⊝⁺ which provide links between the theoretical models and experimental information. We discuss photoproductions and hadron-induced reactions which are useful to explore the nature of ⊝⁺     

SU (8) mass relations amongJ P=1/2+ and 3/2+ baryons

Mass relations among charmed and uncharmed baryons belonging to20 and20′ multiplets of SU(4) are derived in the framework of SU(8) symmetry, Spin singlet mass breaking interaction is found to give unsatisfactory results. Second order effects and spin triplet mass breaking interactions are studied to improve the situation.     

ΔB = −ΔL, neutron →e−π+, e−K+, μ−π+ and μ−K+ decay modes in SU(2)L × SU(2)R × SU(4)col or SO(10)

It is stressed that within the simplest model SU(4) of color, unifying quarks with leptons, where B  L is a gauge symmetry, a spontaneous breaking of this symmetry leads naturally to baryonlepton decays like n→e^?k⁺, e^?K⁺, μ^?π⁺, μ^?K⁺ [in constant to SU(5) where B  L is not gauged]. Our mechanism is crucially tied to the presence of the Higgs multiplet (2, 2, 15) of SU(2) × SU(2) × SU(4), which is needed to account for the observed quarklepton mass ratios.     

Axial Properties of Baryon Ground and Resonant States

We report results from a study of axial charges of baryon ground and resonant states with relativistic constituent quark models. In particular, we consider the axial charges of the octet and decuplet baryons N, ??, ??, ??, ??*, and ??*. The theoretical predictions are compared to experiment, in the case of the N, and to results from other approaches, especially from lattice quantum chromodynamics and chiral perturbation theory. Some remarks are also made regarding the role of axial charges for spontaneous breaking of chiral symmetry.     

Spin,helicity and flavour patterns in exclusive decays of bottom mesons into baryon-antibaryon pairs

I use the constituent quark model to calculate the exclusive decays of bottom mesons into ground state baryon-antibaryon pairs mediated by the weakb→c and b→u transitions. TheW-exchange contributions to these decays are found to be negligible. For theW-decay contributions I find that the simple colour-flavour structure of the 1/2⁺ and 3/2⁺ ground state baryons together with the current-current nonleptonic Hamiltonian leads to many simple and testable predictions. Notable among these is the predicted vanishing of decays involving 3/2⁺ baryons as in \(\overline {B^0 } (B^ - ) \to 3/2^ + \overline {1/2^ + } \) and \(\overline {B^0 } (B^ - ) \to 3/2^ + \overline {3/2^ + } \) . An experimental verification of these selection rules would test the chirality of the basicb→c andb→u transitions. I also derive predictions for the polarization of the final state baryons depending on the assumed mechanism of quark pair creation. These predictions can be checked in the cases where the final state baryons are weakly decaying spin 1/2 hyperons and charmed baryons.     

Nuclearg-factors of theJ π=21/2+isomer in112In and theJ π=6+ 112Sn

Theg-factor of theJ ^π=21/2⁺ isomeric state in¹¹¹In (T _1/2=13.3 ns) and of theJ ^π=6⁺ isomeric state in¹¹²Sn (T _1/2=13.7 ns) were measured using the spin rotation method. The result obtained for theJ ^π=21/2⁺ level in¹¹¹In,g=+0.47 (2), indicates that this state has an almost pure ((πg _9/2)^?1 νg _7/2 νd _5/2) shell model configuration. The experimental valueg=+0.04 (3) for theJ ^π=6⁺ isomer in¹¹²Sn agrees with the theoretical value calculated within the frame of the BCS model.     

Weak decays of charmed baryons

We use the quark model framework to calculate the weak decays of the lowest lying charmed baryons into ground state baryons and mesons. We present detailed results on the predicted flavour and multipole composition of the final state configurations which can be tested in the near future. For the decays 1/2⁺→1/2⁺+0^? we also give symmetry and current algebra estimates which we compare with the quark model results. Semileptonic branching ratios in charmed baryon decays are calculated to be of the order of ～5%. The total lifetime of charmed baryons is predicted to be ～7 10^?14 s which is 5–10 times smaller than the free quark model estimate.     

Soliton models for the nucleon and predictions for the nucleon spin structure

In these lectures the three flavor soliton approach for baryons is reviewed. Effects of flavor symmetry breaking in the baryon wave functions on axial current matrix elements are discussed. A bosonized chiral quark model is considered to outline the computation of spin dependent nucleon structure functions in the soliton picture.     

Polarization of baryons and vector mesons in quark jets ine + e −-annihilation

The cross section and density matrix elements fore ⁺ e ^?→V+X ande ⁺ e ^?→B+X are calculated in the γ-Z ⁰ interference region. The Feynman-Field model for the quark fragmentation functions is extended to include baryons and spin of the particles. Possibilities for obtaining more specific information about the spin dependence of the fragmentation mechanism and the weak coupling of quarks are discussed.     

Colour-exotic constitutent quarks and hadron spectroscopy

Hypothetical colour-exotic constituent (or dressed) quarks are discussed. It is shown that the data on the excited baryons withJ ^P =1/2⁺, 3/2⁺ and excited mesons withJ ^P =0^?, 1^? are in a reasonable agreement with the hypothesis of the existence of colour-exotic quark in the colour state \(\bar 6\) .     

The 27-plet baryons with spin 3/2 under SU(3) symmetry

We investigate the spin-3/2 baryons in the 27-plet based on flavor SU(3) symmetry. For J ^p = 3/2⁺, we find all the candidates for non-exotic members. For J ^p = 3/2^-, we predict a new non-exotic member Λ(1780). Fitting the mass spectrum and calculating the widths of the members show an approximate symmetry of the 27-plet of SU(3). We find that the exotic members have relatively large widths and the Ξ(1950) has spin and parity J ^p = 3/2^-. The possibility of assigning the non-exotic candidates to an octet is also analyzed.     

Magnetic moments of the low lying negative parity Λ resonances

We calculate the magnetic moments of the low lying negative-parity J ^P = 1/2^?, 3/2^? Λ resonances within the framework of chiral constituent quark model. The explicit contribution coming from the valence and sea quarks are being calculated.     

Charmed Mesons in Nuclei with Heavy-Quark Spin Symmetry

We study the properties of charmed pseudoscalar and vector mesons in dense matter within a unitary meson–baryon coupled-channel model which incorporates heavy-quark spin symmetry. This is accomplished by extending the SU(3) Weinberg–Tomozawa Lagrangian to incorporate spin-flavor symmetry and implement a suitable flavor symmetry breaking. Several resonances with negative parity are generated dynamically by the s-wave interaction between pseudoscalar and vector meson multiplets with 1/2⁺ and 3/2⁺ baryons. Those states are then compared to experimental data as well as theoretical models. Next, Pauli-blocking effects and meson self-energies are introduced in a self-consistent manner to obtain the open-charm meson spectral functions in a dense nuclear environment. We finally discuss the formation of D-mesic nuclei.     

Die Hyperfeinstruktur des 32P3/2-Zustands von Natrium im starken Magnetfeld

The hyperfine structure of the 3²P_3/2 State of Na²³has been measured by the optical double resonance technique in a magnetic field of 3.1 kG sufficiently strong to decouple completelyI andJ. In the case of π or (σ⁺+σ^?) excitation the double resonance signal represents the superposition curve of eight unresolved radio-frequency transitions. The dependence of the signal on the pressure of sodium vapour and the radio-frequency field strength has been studied. The analysis of the experimental curves yields for the hyperfine coupling constants the valuesa=(18.7±0.4) Mc/s andb=(3.4±0.4) Mc/s. The nuclear electric quadrupole moment derived from the ratio ofb/a isQ=(0.146±0.02) · 10^?24cm². The Lande factor and the lifetime for the 3²P_3/2state are g_J=1.3344±0.0004 and τ=(1.61±0.07) · 10^?8 sec.     

Heavy Quark Spin Symmetry and Heavy Baryons: Electroweak Decays

Heavy quark spin symmetry is discussed in the context of single and doubly heavy baryons. A special attention is paid to the constraints/simplifications that this symmetry imposes on the non-relativistic constituent quark model wave functions and on the b ?? c semileptonic decays of these hadrons.