Couplings of heavy hadrons with soft pions from QCD sum rules

We estimate the couplings in the Heavy Hadron Chiral Theory (HHCT) lagrangian from the QCD sum rules in an external axial field. We take into account the perturbative correction to the meson correlator in the infinite mass limit. With the perturbative correction and three successive power corrections, the meson correlator in an axial field becomes one of the best known correlators. In spite of this, the corresponding sum rule is not very stable. It yields the result , where is the central value of the heavy meson decay constant with the perturbative correction [14]. This result is surprisingly low as compared with the constituent quark model estimate . The sum rules for following from nondiagonal and diagonal baryon correlators in an external axial field suggest , while diagonal and nondiagonal baryon sum rules have too large uncertainties. Received: 19 June 1997 / Published online: 20 February 1998     

3π强子物理和实验

在强子物理研究中,3π产生的理论和实验有非常重要的意义,是目前世界上很多大型实验设备的重要研究对象。3π强子物理包含丰富的物理内容,可以作为探索低能区强相互作用的有力工具。同时,3π产生过程是寻找奇特轻介子态的主要途径之一。另外,通过研究3π产生反应道还可以寻找“失踪”共振态和重子激发态之间的级联衰变。介绍了目前国际各大高能物理实验室的3π产生过程的实验、理论研究以及分波分析技术现状,重点介绍了美国杰弗逊国家实验室（Jefferson Lab,简称JLab）的CLAS（CEBAF Large Acceptance Spectrometer）实验上的3π反应过程。最后,指出了3π强子物理研究的意义和未来的研究方向。Three pion productions off nucleon are of significance in the research of hadron physics. Meanwhile it is the subject of many big experimental apparatus in the world. Due to the variety of three pion productions, it can be applied as an effective tool to study QCD in low energy region. Three pion productions is one of the main reactions in searching light exotic meson state. Moreover, it is possible to find out the "missing" baryon resonance and the cascaded decay process between baryon excited states. We introduce present experiments and theories of three pion productions as well as the partial wave analysis technique. The emphasis is on the CLAS (CEBAF Large Acceptance Spectrometer) experiment at JLab (Jefferson Lab). In the end, we point out the significance of studying the three-pion hadron physics at JLab.     

Structure of hadron beam jets at smallP T

A dynamical model of hadron beam jets in high energy hadron-hadron collisions at smallp _T is presented on the basis of the assumptions that (i) a meson is composed of a constituent quarkq and an antiquark \(\bar q\) , while a baryon is composed ofq andqq (diquark), and (ii) mesons, baryons and antibaryons are emitted via the cascade mechanism ofq andqq. These assumptions lead to a simple treatment of meson, baryon and antibaryon productions from hardon beam jets. A set of coupled integral equations for \(\bar q\) andqq fragmentation functions is solved in moment space and converted into the longitudinal distribution. Inclusive spectra of hadrons directly produced from beam jets are compared with data.     

Spinor strong interaction model for baryon spectra

The spinor strong interaction model recently proposed by the author to account for meson spectra is applied to baryons. Quark-quark strong interaction is of massless scalar type. Harmonic confinement arises as naturally as linear confinement for mesons. No approximation is needed in order to derive, from the proposed covariant spinor baryon equations, coupled nonlinear radial equations for the ground-state spin-1/2 and spin-3/2 baryons in the rest frame. These equations are effectively of sixth order and call for a particle classification other than the usual unrelativistic one. Simplified analytical solutions are given. Internal functions and mass operators are analogously introduced. With these and the above simplified space-time solution, baryon data yield bare quark masses that agree approximately with those analogously obtained earlier from meson data.     

Quark recombination in deuteron fragmentation

Low-P _T production off deuteron in the fragmentation region is studied on the basis of a six-quark picture of deuteron. It is argued that all the six valence quarks participate equally in the hadronization processes associated with meson and baryon productions. Thex-distribution of the inclusive cross sections is studied in the framework of a quark recombination model. Fit with experimental data leads to a determination of the valence and sea quark distributions in deuteron. Probabilistic arguments applied to a general recombination picture are shown to lead to some experimentally verifiable constraints on baryon multiplicities. Possibilities of determining the various recombination probabilities are also discussed.     

η-production on the proton via electromagnetic and hadronic probes

The reactions π-p →ηn and γ＇p →ηP are investigated within a dynamical coupledJchannels model of meson production reactions in the nucleon resonance region. The meson-baryon channels included are πN, ηN, π△, σN, and pN. The direct wphotoproduction process is studied within a formalism based on a chiral constituent quark model approach, complemented with a one-gluon-exchange mechanism, to take into account the breakdown of the SU（6）0（3） symmetry. In the models search, the following known nucleon resonances are embodied： Sll （1535）, $11（1650）, Pll （1440）, Pl1（1710）, P13（1720）, D13（1520）, D13（1700）, D15（1675）, and F15（1680）. Data for the π-p →ηnreaction from threshold up to a total center-of-mass energy of W ≈ 2 GeV are satisfactorily reproduced. For the photoproduction channel, two additional higher mass known resonances, P13 （1900） and F15 （2000）, are also considered. However, reproducing the data for γ＇p →ηP requires, within our approach, two new nucleon resonances, for which we extract mass and width.     

Nuclear Matter in a Chiral SU(3) Quark Mean-Field Model

A quark meson coupling model based on SU(3)_L×SU(3)_R symmetry and scale invariance is proposed. The quarks and mesons get masses through symmetry broken. We apply this SU(3) chiral constituent quark model to investigating the nuclear matter at finite temperature and density. The effective baryon masses, compression modulus and hyperon potentials are all reasonable. The critical temperature of liquid-gas phase transition is also calculated in this model.     

夸克平均场模型的有限核及超核研究

夸克平均场模型采用组分夸克模型描述重子,已被用于研究有限核及超核的性质.介子平均场直接与核子内的组分夸克相互作用,从而改变了核介质内重子的性质.夸克平均场模型能够给出令人满意的球型核及超核的性质,该模型也预言了核介质中核子体积的膨胀及核子有效质量的降低.     

Meson cloud and SU(3) symmetry breaking in parton distributions

We apply the meson cloud model to the calculation of non-singlet parton distributions in the nucleon sea, including the octet and the decuplet cloud baryon contributions. We give special attention to the differences between non-strange and strange sea quarks, trying to identify possible sources of SU(3) flavor breaking. An analysis in terms of the parameter is presented, and we find that the existing SU(3) flavor asymmetry in the nucleon sea can be quantitatively explained by the meson cloud. We also consider the baryon, finding similar conclusions. Received: 28 July 2000 / Published online: 23 October 2000     

夸克平均场模型研究有限核及超核

采用组分夸克模型描述重子,首先由自由核子及超子的性质定出模型参数,进一步考虑核介质中重子性质的变化,核介质中的介子平均场直接与重子内部的组分夸克相互作用.夸克平均场模型已被用于研究有限核及超核的性质,能够给出令人满意的有限核及超核的性质,该模型也预言了核介质中核子体积的膨胀及核子有效质量的降低. The quark mean field model, which describes the baryon by using the constituent quark model, is applied to study the properties of finite nuclei and hypernuclei. The meson mean fields couple directly with the quarks and change the properties of baryons in nuclear medium. The quark mean field model provides satisfactory results on the properties of spherical nuclei and hypernuclei. It also predicts an increasing size of the nucleon as well as a reduction of the effective mass in the nuclear environment.     

SU(2) Yang-Mills theory in (1 + 1) dimensions: A finite-lattice approach

Finite-lattice methods are used to calculate the masses of the lowest-lying baryon and meson states in the two-dimensional SU(2) Yang-Mills theory. No sign of a phase transition is seen at non-zero quark mass m. Both the meson and baryon mass vanish at m = 0: this is presumably a “chiral protection” mechanism.     

Hadronic decays of N and Δ resonances in a chiral quark model

π and η decay modes of light baryon resonances are investigated within a chiral quark model whose hyperfine interaction is based on Goldstone-boson exchange. For the decay mechanism a modified version of the ³ P ₀ model is employed. Our primary aim is to provide a further test of the recently proposed Goldstone-boson exchange constituent quark model. We compare the predictions for π and η decay widths with experiment and also with results from a traditional one-gluon exchange constituent quark model. The differences between nonrelativistic and semirelativistic versions of the constituent quark models are outlined. We also discuss the sensitivity of the results on the parameterization of the meson wave function entering the ³ P ₀ model. Received: 11 May 2001 / Accepted: 17 September 2001     

COMPOSITE PARTICLE REPRESENTATION METHOD FOR BARYON SPECTRUM

In this paper, the baryon is regarded as a two-body system which consists of a diquark and a quark. The baryon spectrum is calculated by means of the composite particle represenEation based on the nonrelativistic potential model.The effectfve quark potential is determined by fitting the meson spectrum. Therefore, there is only one adjustable parameter in the calculations, and that is the harmonic oscillator frequency. ω in the single-quark basis. The theoretical results are reasonably consistent with the experimental data.     

Time-Odd Component and its Influence on the Properties of 41Ca

The triaxial deformed Relativistic Mean Field (RMF) model including the time-odd component is developed. The magnetic potential and baryon current in ⁴¹Ca and their influence on the magnetic moment, single particle level splitting for time reversal states and other properties are investigated in triaxial deformed RMF model with the spatial-component of vector meson fields by using PK1 effective interaction, which includes the self-coupling of σ and ω meson fields as well as the microscopic correction for the center of mass.     

Effects on the Hadron Propagators due to κμκυ Terms in the Vector Meson Propagator

In an approximation where the baryon current conservation is violated, the contribution of the κμκυ terms in the vector meson propagator may not vanish. Their effects on the baryon and meson spectral functions and on the consequences of self-consistency are studied in the relativistic self-consistent Hartree-Fock approximation by means of the σ-ω model. Two cases where the κμκυ terms are and are not neglected are compared. It is found that there is a marked change in the baryon spectral function which becomes more peaked in the latter case. Such a change remains even by a proper readjustment of parameters. The effects of self-consistency in the σ-ω model are qualitatively the same in both cases, though quantitatively there is some significant difference.     

Recent progress on the chiral unitary approach to meson meson and meson baryon interactions

We report on recent progress on the chiral unitary approach, analogous to the effective range expansion in Quantum Mechanics, which is shown to have a much larger convergence radius than ordinary chiral perturbation theory, allowing one to reproduce data for meson meson interaction up to 1.2 GeV. Applications to physical processes so far unsuited for a standard chiral perturbative approach are presented. Results for the extension of these ideas to the meson baryon sector are discussed, together with applications to kaons in a nuclear medium and K⁻ atoms.     

Extraction of resonance parameters from meson production reaction

We have developed an analytic continuation method for extracting parameters of nucleon resonances within a Hamiltonian formulation of meson-nucleon reactions. The method was tested for simple solvable models and then applied for our recent coupled channels model （πN, ηN, π△, ρN, and σN ） of the π＊N and γ＊N reactions. The resonance pole positions and their properties are studied for P11and P11 channels.     

Recent results for single meson production from the Crystal-Barrel/TAPS experiment at ELSA

The present focus of the CBELSA/TAPS experiment is on meson-photoproduction off the nucleon using polarized photons and polarized targets. Here first preliminary results on the reactions γp → pπ and γp → pπ for both circularly and linearly polarized photons and a longitudinally polarized target are presented. Preliminary results for the beam asymmetry ∑ and the double polarization observable G have been extracted for both reactions using the linear polarization data. From the circular polarization data the observable E has been determined. Due to the near 4π angular coverage of the detector system these results cover almost the full solid angle.     

THE WAVE EQUATIONS AND MASS SPECTRA OF BARYON STATES IN THE QUARK MODEL

The independent particle approximation is used to treat the bound state problems in the quark model. The solution for meson states obtained in this approximation is the same as that obtained from the Bethe-Salpeter equation. The solution for the baryon states is also obtained. The mass spectra of mesons and baryons determined from these equations are in agreement with the experiment.