Hadron clusters with quark core and multiplicity distributions

Multiplicity distributions of ground state hadrons (pseudoscalar and vector meson nonet and baryon octet and decuplet) are investigated in a model of hadron clusters based of subsequent hadron emission by quarks. The effects of resonance decay for the observed (stable) hadron multiplicities are also considered. Average numbers of different hadrons are calculated as a function of the number of charged pions. The results are compared with available data and a good overall agreement is found.     

Point-Form Hamiltonian Dynamics and Applications

This short review summarizes recent developments and results in connection with point-form dynamics of relativistic quantum systems. We discuss a Poincaré invariant multichannel formalism which describes particle production and annihilation via vertex interactions that are derived from field theoretical interaction densities. We sketch how this rather general formalism can be used to derive electromagnetic form factors of confined quark?Cantiquark systems. As a further application it is explained how the chiral constituent quark model leads to hadronic states that can be considered as bare hadrons dressed by meson loops. Within this approach hadron resonances acquire a finite (non-perturbative) decay width. We will also discuss the point-form dynamics of quantum fields. After recalling basic facts of the free-field case we will address some quantum field theoretical problems for which canonical quantization on a space?Ctime hyperboloid could be advantageous.     

Masses of S and P wave mesons and pseudoscalar decay constants using a confinement scheme

In the framework of relativistic harmonic confinement model for quarks and antiquarks, the masses of S- and P-wave mesons and pseudoscalar decay constants from light flavour to heavy flavour sectors are computed. The residual two-body Coulomb interaction and the spin-dependent interaction of the confined one gluon exchange effects (COGEP) such as spin-spin and spin-orbit interactions are perturbatively incorporated with the confinement energy to get the respective vector-pseudoscalar meson mass differences. Here we employ the same parametrization and model parameters as used in a recent study of low-lying hadron masses and leptonic decay widths. The results are being compared with the values obtained from other theoretical models and the experimental values.     

弹性e-d散射中氘核的张量极化t20与ρπγ耦合过程

在夸克-强子混杂模型基础上，利用氘核的相对论波函数，计及冲击近似、ρπγ过程贡献和6夸克集团效应， 计算了氘核的张量极化t20. 结果表明， 当ρπγ耦合常数取正值时， t20的理论值才与新扩展的实验数据符合. Tensor polarization t20 of the deuteron is calculated on the basis of a hybrid quark hadron model. A relativistic wave function of the deuteron is used to calculate the relativistic impulse approximation and the contribution of the ρπγ meson exchange process. Good agreement with experimental data is achieved when and only when the ρπγ coupling constant is taken as positive.     

Meson Cloud Effect on △(1232) Resonance Transition Properties with a Relativistic Quark Model Approach

Based on a relativistic quark model approach, the transition properties of the first nucleon resonance △(1232), and the coupling constants gπNN, g△πN are investigated. Tvo different vays to remove the center of mass motion are considered. The results of the relativistic approaches with and without center ofmass correction are compared with those of nonrelativistic constituent quark model. Moreover, pion meson cloud effect on these calculated observables is explicitly addressed. Better results are obtained by taking the pion meson cloud into account.     

Meson Cloud Effect on Δ(1232) Resonance Transition Properties with a Relativistic Quark Model Approach

Based on a relativistic quark model approach, the transition properties of the first nucleon resonance Δ(1232), and the coupling constants g_πNN, g_ΔπN are investigated. Two different ways to remove the center of mass motion are considered. The results of the relativistic approaches with and without center of mass correction are compared with those of nonrelativistic constituent quark model. Moreover, pion meson cloud effect on these calculated observables is explicitly addressed. Better results are obtained by taking the pion meson cloud into account.     

利用波函数研究Bc介子纯轻衰变的QCD非微扰特性

B_c介子辐射性纯轻衰变的理论计算具有很大的强子型不确定性。利用3种类型的B_c介子波函数描述这种纯轻衰变的QCD非微扰特性, 并通过控制函数中参数的变化在理论上详细地计算了由介子波函数而引起的B_c介子辐射性纯轻衰变的这种强子型的不确定性。 结果表明,介子波函数的形式对计算的衰变结果有非常明显的影响, 该过程的分支比可在1.819 81×10-5～3.189 61×10-5间变化。 The radiative and pure leptonic decays of B_cmesons are of hadrons uncertainty in theoretical calculations. Using three types of the B_c meson wave functions which describe the characteristics of the QCD non perturbative and by controlling the parameters in them, the uncertainties of B_c meson decay caused by the hadron decay model are studied in detail. The theoretical results show the branching ratios are (1.819 81~3.189 61)×10-5, which are sensitive to the type of wave functions.     

Description of isovector giant dipole resonances in relativistic Vlasov equation at small amplitude limit

A more general relativistic Vlasov equation has been derived in the framework of relativistic quantum hadron dynamical theory. In the small amplitude limit we use this Vlasov equation to study the isovector giant dipole resonances built on groundstate in spherical nuclei¹⁶O,⁴⁰Ca,⁹⁰Zn and²⁰⁸Pb. The results show that the spin-orbit coupling and the non-linear terms of scalar meson can influence the resonance energies to a certain extent comparing with those obtained from the non-relativistic Vlasov equation approach and are in good agreement with the experimental ones, especially for the case which vacuum fluctuation is included.     

Pion emission in α-particle interactions with various targets of nuclear emulsion detector

The behavior of relativistic hadron multiplicity for4He-nucleus interactions is investigated. The experiment is carried out at 2.1 A and 3.7 A Ge V(Dubna energy) to search for the incident energy effect on the interactions inside different emulsion target nuclei. Data are presented in terms of the number of emitted relativistic hadrons in both forward and backward angular zones. The dependence on the target size is presented. For this purpose the statistical events are discriminated into groups according to the interactions with H, CNO, Em, and Ag Br target nuclei. The separation of events, into the mentioned groups, is executed based on Glauber's multiple scattering theory approach. Features suggestive of a decay mechanism seem to be a characteristic of the backward emission of relativistic hadrons. The results strongly support the assumption that the relativistic hadrons may already be emitted during the de-excitation of the excited target nucleus, in a behavior like that of compound-nucleus disintegration.Regarding the limiting fragmentation hypothesis beyond 1 A Ge V, the target size is the main parameter affecting the backward production of the relativistic hadron. The incident energy is a principal factor responsible for the forward relativistic hadron production, implying that this system of particle production is a creation system. However, the target size is an effective parameter as well as the projectile size considering the geometrical concept regarded in the nuclear fireball model. The data are analyzed in the framework of the FRITIOF model.     

袋模型进展

本文回顾了强子结构袋模型几年来所取得进展,着重介绍近两年来的进展。总结是沿以下三个方面进行的,(一)理论描述的进一步完善,包括半定量地介绍了R.L.Jaffe等人最近提出的,考虑到手征对称的混合袋模型。(二)袋模型对强子静态性质的应用,包括轻夸克强子和重夸克强子的质量谱,以及对π介子质量的重新考虑。(三)多夸克强子,分析了它们分类情况,并估计了它们的质量。袋模型对于强子衰变,强子碰撞等动态过程,以及对原子核的应用成就不多,进展不大,而且篇幅有限,未作定量介绍。     

Thermodynamics of hadronic matter at high density

We calculate thermodynamics observables for an interacting relativistic hadron gas. Hadronic states are taken into account by the use of a sizeable portion of the experimental hadron spectrum, supplemented in some cases by an exponentially rising continuum. Calculations with non-zero baryon number densities, subject to the additional requirement of zero net strangeness, show structure in the heat capacity per unit volume of the baryon sector at a temperature of approximately 140 MeV. This structure also becomes visible in the total heat capacity per unit volume at large baryon number densities, and provides a signature for the change of the thermal response of the hadron gas from baryon- to meson-dominated, even though the meson number density is lower than the baryon number density. Furthermore, this structure is not seen in calculations with a massless hadron gas. Its origin is therefore associated with information contained in the hadronic mass spectrum, and thus with the sub-hadronic degrees of freedom of the hadrons.     

Central exclusive meson pair production in the perturbative regime at hadron colliders

The central exclusive production (CEP) of heavy resonance states that subsequently decay into meson pairs, \(M\overline{M}\), is an important signature for such processes at hadron colliders. However, there is a potentially important background from the direct QCD production of meson pairs, as mediated for example by the exclusive \(gg\to M\overline{M}\) hard scattering subprocess. This is in fact an interesting process in its own right, testing novel aspects of perturbative QCD technology. We explicitly calculate the \(gg \to M\overline{M}\) helicity amplitudes for different meson states within the hard exclusive formalism, and comment on the application of MHV techniques to the calculation. Using these results, we describe how meson pair CEP can be calculated in the perturbative regime, and present some sample numerical predictions for a variety of final states. We also briefly consider the dominant non-perturbative contributions, which are expected to be important when the meson transverse momentum is small.     

巨共振激发的相对论效应

在相对论量子场论（ＱＨＤ）的框架下,得到了相对论线性Ｖｌａｓｏｖ方程．依此计算了球形核１６Ｏ、４０Ｃａ、９０Ｚｒ及２０８Ｐｂ的巨偶极共振的强度函数分布．结果表明,相对论效应是不可忽视的．计算得到的巨共振中心能量稍高于非相对论线性Ｖｌａｓｏｖ方程给出的对应值,与实验结果比较都有较好的符合．对计算结果作了简要的讨论,发现核子有效质量和平均场自旅轨道耦合力对巨共振能量有重要影想． In the framework of relativistic quantum hadron dynamical (QHD) theory,under semiclassical approximation and taking into vacuum fluctuation, a relativistic Vlasov equation (RVE) has been derived. Using RVE and considering other relativistic effects, we have studied the isovector dipole giant resonances built on ground state in spherical nuclei.The main results show that the resonance energies for each multipole are larger than those obtained from the non-relativistic classical Vlasov approach...     

Production of hadron resonances in heavy-ion collisions

The role of microscopic kinetics in the production of short-lived (broad) hadron resonances from subhadronic nuclear matter is considered. Anew approach to calculating the multiplicity of broad meson resonances is proposed. This approach takes explicitly into account the possibility that massive constituent quarks play a decisive role at the last stage of the expansion and cooling of matter produced in the central collisions of relativistic heavy nuclei. The resulting theoretical estimates are comparedwith available experimental data, and some quantitative and qualitative predictions are made.     

Masses and electroweak properties of light mesons in the relativistic quark model

The masses, pseudoscalar and vector weak decay constants and electromagnetic form factors of light S-wave mesons are studied in the framework of the relativistic quark model based on the quasipotential approach. We use the same model assumptions and parameters as in our previous investigations of heavy meson and baryon properties. The masses and wave functions of the ground state and radially excited π, ρ, K, K^* and φ mesons, obtained by solving numerically the relativistic Schrödinger-like equation with the complete relativistic qq? potential including both spin-independent and spin-dependent terms, are presented. Novel relativistic expressions for the weak decay constants of the pseudoscalar and vector mesons are derived. It is shown that the intermediate negative-energy quark states give significant contributions which essentially decrease the decay constants bringing them in agreement with experimental data. The electromagnetic form factors of the pion, charged and neutral kaon are calculated in a broad range of the space-like momentum transfer. The corresponding charge radii are determined. All results agree well with the available experimental data.     

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.     

Hadrons and broken symmetries with WASA-at-COSY

The WASA Detector Facility is an internal experiment at the cooler synchrotron (COSY) in Jülich, Germany. The COSY accelerator provides proton and deuteron beams with momenta up to 3.7 GeV/c giving access to hadron physics including the strange quark sector. The physics program with the WASA detector involves hadron dynamics and hadron structure. Key experiments address fundamental symmetries and symmetry violations via the study of rare and not-so-rare meson decays. From the very first production run, results on the Dalitz plot slope parameter in the isospin violating η → 3π ⁰ decay have been obtained. The 3π ⁰ final state is also used to study meson production mechanisms. Investigations of other decay modes of the η-meson address C, P, and T symmetries and combinations. Higher orders in chiral perturbation theory are probed with the η → π ⁰ decay. The status and plans for studying hadron structure with Dalitz decays of mesons are presented.     

Proton decay in terms of an effective baryon-lepton transition

We calculate the two-body decay rates for the hadronic and electromagnetic decays of proton and neutron in terms of the effective baryon-lepton transition matrix element. Further ingredients like PCAC and vector meson dominance are used. We compute these transition amplitudes within the framework of a relativistic quark model involving Bethe-Salpeter amplitudes and present the nucleon lifetimes and branching ratios of various decay modes for three different grand unification models.     

Towards transport theory of hadron gases

An important role of hadron resonances for determining the characteristics of hadron gases is argued. A kinetic theory model of hadron gas is developed. A classical, nonquantum, distribution function of a resonance is defined with the help of the profile function being an analogue of the mass shell delta function of stable particles. The Boltzmann equation is generalized to include the resonance decay and resonance formation processes. To determine the unknown profile function, the transition rates are assumed to satisfy the bilateral normalization or the detailed balance condition. The profile function is expressed through the resonance formation cross section and the decay width. The H-theorem is proved, and it is shown that the form of the equilibrium distribution function of a resonance coincides with that of a stable particle. Macroscopic equilibrium characteristics are studied. Significance of the resonance mass smearing effect is demonstrated.