Baryon properties in the relativistic quark model

Properties of heavy and strange baryons are investigated in the framework of the relativistic quark-diquark picture. It is based on the relativistic quark model of hadrons, which was previously successfully applied for the calculation of meson properties. It is assumed that two quarks in a baryon form a diquark and baryon is considered as the bound quark-diquark system. The relativistic effects and diquark internal structure are consistently taken into account. Calculations are performed up to rather high orbital and radial excitations of heavy and strange baryons. On this basis the Regge trajectories are constructed. The rates of semileptonic decays of heavy baryons are calculated. The obtained results agree well with available experimental data.     

Baryon multipole moments in the single quark transition model

It is shown that the predictions of the single quark transition model of the electromagnetic transitions of baryons can be expressed in a highly simplified form by the simultaneous use of multipole moments at the quark level and at the baryon level. The predictions so expressed are applied to the latest ‘world average’ photoproduction amplitudes and an excellent fit is obtained. The model also fits electroproduction amplitudes to within the errors. It is argued that the electromagnetic decays of baryon resonances to dileptons are of particular interest and widths for these processes are estimated.     

Baryon exotics in the quark model, the skyrme model, and QCD

We derive the quantum numbers of baryon exotics in the quark model and the Skyrme model and show that they agree for arbitrary colors and flavors. We define exoticness E, which can be used to classify the states. The exotic baryons include the recently discovered qqqqq pentaquarks (E=1), as well as exotic baryons with additional qq pairs (E>/=1). The mass formula for nonexotic and exotic baryons is given as an expansion in 1/N(c) and allows one to relate the moment of inertia of the Skyrme soliton to the mass of a constituent quark.     

The extended quark sigma model at finite temperature and baryonic chemical potential

An extended quark sigma model which includes higher-order mesonic interactions is studied at the finite baryonic chemical potential u _B and temperature T. The field equations have been solved in the mean-field approximation by using the modified iteration method at finite baryonic chemical potential u _B and temperature T. The Goldstone theorem is satisfied below a critical temperature in the chiral limit for u _B = 0. As expected from general universality, the chiral phase transition is second-order. By including the higher-order mesonic interactions, the critical temperature is reduced compared to that found in recent works and is in good agreement with lattice QCD results. The nucleon mass is examined in the (u _B , T) plane, showing a strong dependence on u _B and T. We find that an increase in both the baryonic chemical potential u _B and the temperature T leads to an increase in the values of the nucleon mass. This is evidence for the quark-gluon deconfinement phase transition at higher values of temperature.     

Three to six ambiguities in immittance spectroscopy data fitting

Several important ambiguities in immittance spectroscopy (IS) model data-fitting results are identified and illustrated by means of complex-nonlinear-least-squares (CNLS) fits of experimental and synthetic frequency response data. A well-known intrinsic ambiguity, following from Maxwell's electromagnetic equations, arises from the indistinguishability in external measurements of conduction and displacement currents. Usual fit models for either dielectric or conductive-system situations, such as the Davidson-Cole one, only involve a strength parameter, a dielectric constant, a characteristic relaxation time, and a fractional exponent and lead to no additional ambiguities. But the situation is different for more powerful and useful general models, such as ordinary or anomalous diffusion Poisson-Nernst-Planck ones: PNP and PNPA, used here, whose historical background, current status, and applicability are described and discussed herein. They apply to two different kinds of experimental IS situations and involve several additional, potentially free fit parameters, such as the mobilities of positive and negative charge carriers, and generation-recombination parameters that determine the partial or complete dissociation of a neutral entity of concentration N(0) into positive and negative charge carriers of equal concentration, c(0). Then, several additional ambiguities appear that may require information about the material system involved for their adequate resolution.     

Properties of quark matter governed by quantum chromodynamics (II). Renormalization schemes in quark matter

Renormalization schemes are examined (in the Coulomb gauge) for quantum chromodynamics in the presence of quark matter. We demand that the effective coupling constant for all schemes become congruent with the vacuum QCD running coupling constant as the matter chemical potential, μ, goes to zero. Also, to enable us to standardize with the vacuum QCD running coupling constant at some asymptotic momentum transfer, $\text{|}\text{p}{}_0\text{|,}\text{we keep}\text{μ ? ¦}\text{p}{}_0\text{¦}$, to ensure that the matter contribution is negligible at this point. This means all schemes merge with vacuum QCD at $\text{|}\text{p}{}_0\text{|}$ and beyond. Two renormalization group invariants are shown to emerge: (i) the effective or invariant charge, g_inv², which is, however, scheme dependent and (ii) g²(M)/S(M), where S(M)^?1 is the Coulomb propagator, which is scheme independent. The only scheme in which g_inv² is scheme independent and identical to g²(M)/S(M) is the screened charged scheme (previous paper) characterised by the normalization of the entire Green function, S^?1, to unity. We conclude that this is the scheme to be used if one wants to identify with the experimental effective coupling in perturbation theory. However, if we do not restrict to perturbation theory all schemes should be allowed. Although we discuss matter QCD in the Coulomb gauge, the above considerations are quite general to gauge theories in the presence of matter.     

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     

Re-analysis of the baryon mass spectrum using the quark shell model

Detailed numerical comparison of the baryon mass spectrum analysis of Jones, Levi Setti and Lasinski with that of Horgan has led to a deeper understanding of the formulae and techniques used in both analyses. In this light, we have re-analysed the baryon mass spectrum for the (70, 1^?)₁ and (56/70, 2⁺)₂ multiplets updated to include the most recent PDG data and have checked the results for the (70, 1^?)₁ using two independent computer programmes. The predicted spectra obtained are presented and the classification of the states is compared with that of a recent decay analysis by Hey, Litchfield and Cashmore.     

Polarization predictions and the quark and peripheral models

Inconsistencies and ambiguities in the interpretation of quark-model predictions for decay correlations in resonance production are discussed. A proper relativistic treatment shows which predictions from the non-relativistic model can be expected to hold at relativistic energies where experimental tests are made. The existence of reasonable peripheral models which lead to the same predictions is pointed out, thus indicating that success of the predictions is not nesessarily evidence supporting the quark model.     

Calculable observables in quantum chromodynamics: (II). Heavy quark production

It is argued that the color-averaged inclusive cross section dσ/d³p for the production of a heavy quark of given momentum p and given flavor is infrared-singularity free and therefore calculable in perturbative QCD if it is evaluated away from heavy quark thresholds and if the typical reaction energy Q is such that α_s(Q)ln[Q/m(Q)] is small, α_s and m being the strong coupling constant and the heavy quark mass respectively. An interpretation of this cross section is proposed in terms of heavy flavor hadronic production.     

Non-linear quark theory of spin 2 fields (gravitational mesons). II

An equation for spin 1/2⁺ and 3/2⁺ fermions interacting with a 27-plet of gravitational mesons is derived by the confluence method in the framework of non-linear quark theory of elementary particles. The case of spin 1/2⁺ baryons is examined in detail, and the equation for the baryon octet is derived in the form of an equation for a spinor field in curved space (the Fok-Ivanenko equation). An effective metric is defined by means of the 27-plet of gravitational mesons.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 7–11, April, 1973.     

Multi-nucleon transfer spectroscopy in the shell model

Formulas for calculating multi-nucleon transfer spectroscopic amplitudes tailored for use with the Rochester-Oak Ridge shell-model computer programs are presented. Expressions are given for the evaluation of three- and four-particle coefficients of fractional parentage. Predictions of α-particle spectroscopic factors for ${}^{58}\text{Ni}\text{+ α →}{}^{62}\text{Zn}\text{,}{}^{60}\text{Ni}\text{+ α →}{}^{64}\text{Zn}\text{,}\text{and}{}^{40}\text{Ca}\text{+ α →}{}^{44}\text{Ti}$ are compared with experiment.     

利用电子结构数据拟合H2分子的电子壳模型势函数参数

电子壳模型势函数在离子晶体的原子级计算机模拟中有广泛应用,其势参数主要通过拟合晶体的实验数据或电子结构数据得到.提出了通过拟合双原子分子的量子化学从头计算电子结构数据来获得该势函数的方法,并由H2分子的电子结构数据建立了H原子间的电子壳模型势函数.此外,还应用该势函数对H+2分子离子进行了计算.该势函数拟合方案更适合于共价键型的分子.     

Quadrupole excitations in the two-center shell model (II)

The distribution of the isoscalar, T = 0, and isovector T = 1, strength of quadrupole modes in the deformed nucleus ²⁴Mg is investigated. A finite-range residual interaction is used in the particle-hole basis of a rotating two-center shell-model potential of two ¹²C nuclei. The model calculation describes semi-quantitatively the main features of the available experimental data for the T = 0, E2 excitations and predicts the location and structure of the isovector, T = 1, E2 strength for which no data has been published to date.     

Direct-search methods in data fitting: Application to Mössbauer spectroscopy

Summary An algorithm based on the direct search of parameter optimization without evaluating derivatives is discussed. It consists of a slightly modified version of the Hooke and Jeeves method, optimized in velocity, in order to give quick rensponses also on personal computers. In the present work it has been applied to the minimization of a sum of squares, common case in data fitting. An application to M?ssbauer spectroscopy is presented.     

Fit of the mixing angles in the six quark model and predictions on theB meson lifetime

Experimental data are used to constrain the parameters of the six quark mixing model and of a composite quark model. A combined fit of the mixing angles in the Kobayashi-Maskawa scheme gives sinθ ₁=0.228±0.011 and error contours around the best values sinθ ₂=0.12 and sinθ ₃≈0. From this, a limit of τ _B >0.35×10^?13 s for the mean lifetime of bottom-flavoured hadrons is obtained. For the composite quark model of Katsumata and Tomozawa, a value of τ _B =(0.22?0.23)10_?13 s is derived.