介子束缚态相对论本征方程的非微扰重整化

介子结合态本征方程中δ相互作用可用T矩阵进行非微扰重整化,深入理解重整化的一些基本问题:物理结果与重正化点的选取无关,T矩阵非微扰重整化的物理实质. Nonperturbative T-matrix renormalization of the relativistic eigen equation for meson mass spectra is described and the expressions for eigen mass spectra and eigen wave functions are given.     

Influence of In-medium properties of vector mesons on dilepton production in heavy ion collisions at SIS energies

Dileptons represent a unique probe for nuclear matter under extreme conditions reached in heavy ion collisions. They allow the study of meson properties, like mass and decay width, at various density and temperature regimes. Up to now, in the Tübingen model for dilepton production, modification of meson properties in nuclear medium has been accounted for by allowing a density dependence of the mass (Brown–Rho scaling) together with an ad hoc dependence of the meson decay widths on the same variable. We use the extended vector meson dominance (eVMD) model to extract meson properties in nuclear matter by computing the in-medium meson spectral functions. Dilepton spectra for C+C at 1.0 and 2.0 AGeV are calculated and compared with previous results.     

Meson spectra governed by the Fermi-Breit potential

We calculate the meson mass spectra in a quark potential model by using the complete Fermi-Breit potential including the terms of orbit-orbit interaction, spin-orbit coupling, and tensor force interaction. We find that these terms give nontrivial contributions to the calculated meson spectra. The orbit-orbit coupling term may lead to an instability of the solution of the Schrodinger equation and should be regularized.     

Algebraic meson models

We discuss two meson models where a meson is described in the Bethe-Salpeter formalism as a bound state of a quark and an antiquark interacting via an instantaneous infinite square-well potential. In the first model the quark and antiquark are heavy and the depth of the potential exactly balances their rest energy and in the second model the quark and antiquark are massless. In each model the mass operator for the composite system is homogeneous. Hence a dilatation operator can be defined such that the mass operator transforms in the same way as the translation generator under infinitesimal scale transformations. Then the quark-antiquark bound states carry irreducible representations of the Weyl Lie algebra which, due to the scale parameter introduced by the finite width of the infinite square-well potential, have nontrivial discrete mass spectra.     

Observation of rho/omega meson modification in nuclear matter

We measured the invariant mass spectra of electron-positron pairs in the target rapidity region of 12-GeV p+A reactions. We have observed a significant difference in the mass spectra below the omega meson between p+C and p+Cu interactions. This difference indicates that the spectral shape of mesons is modified at normal nuclear-matter density.     

Evidence for in-medium modification of the phi meson at normal nuclear density

Invariant mass spectra of e(+) e(-) pairs have been measured in 12 GeV p + A reactions to detect possible in-medium modification of vector mesons. Copper and carbon targets are used to study the nuclear-size dependence of e(+) e(-) invariant mass distributions. A significant excess on the low-mass side of the phi meson peak is observed in the low betagamma(= beta/square root(1-beta(2))) region of phi mesons (betagamma < 1.25) with copper targets. However, in the high betagamma region (betagamma > 1.25), spectral shapes of phi mesons are well described by the Breit-Wigner shape when experimental effects are considered. Thus, in addition to our earlier publications on rho/omega modification, this study has experimentally verified vector meson mass modification at normal nuclear density.     

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.     

Theoretical analysis of dilepton spectra in heavy ion collisions at GSI-FAIR energies

This paper addresses the theoretical analysis of dilepton spectra in C+C collisions at GSI-SIS energies. Theoretical predictions for the recent data of the HADES Collaboration at SIS energies are made with the help of a hadron-string transport model, the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model. A mass shift of the ρ meson due to kinematical effects is discussed.     

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.     

Determination of meson resonance contributions to pion and kaon inclusive spectra

π- andK-meson inclusive spectra with low transverse momenta inK-meson fragmentation region inKp-interactions are determined on the basis of the assumption on a recombination mechanism of hadron production. It is shown that the pion and kaon spectra (both “direct” and from resonance decay) inK-meson fragmentation region can be expressed by structure functions of initialK-meson. Contributions from resonance decays from different meson multiplets (vector, axial and tensor) to pion and kaon inclusive spectra are determined. α=(3A _T /5A _V )=0.28±0.02 is found for the suppression factor ofP-wave meson state production as compared to theS-wave one. It is shown that with decreasing final meson mass the relative contribution of direct production to meson inclusive spectrum increases. In the limits of available experimental errors in meson resonance spectra there is found no dependence of meson yields on the value of summary spin of quark and antiquark producing meson (β=3A _P /A _V =1). It is shown that analysis of meson resonance inclusive spectra allows one to determine not only the parameters of valence quark distribution in the initialK-meson but also the sea parton distributions. For the strange sea quark distribution inK-meson there is founds _S(x) ～(1?x) ^ns wheren _S =4.8±1.0, which agrees with the prediction of the quark counting rules for this quantity.     

The Strong Interaction in Chromodynamics Ⅱ

A static soliton solution is obtained from the field equations of chromodynamics. The relativistic wave equation for meson states in which the quark and antiquark interact through the intermediary of this gluon field gives rise. to the same wavefunction and mass spectra obtained before under the independent particle approximation. The calculated values of mass difference of η_c and Ψ/J particles and mass difference of Ψ(3685) and Ψ(3770) due to spin-dependent part of the interaction are in good agreement with the experiment.     

Spinor strong interaction model for meson spectra

A model for a bound quark-antiquark system is constructed from quark spinor equations and the associated pseudoscalar massless interaction potential equations in a way departing from conventional relativistic quantum mechanics. From the so-constructed covariant meson equations, linear confinement arises naturally. Nonlinear radial equations for the pseudoscalar and vector mesons in the rest frame are derived without approximation. An internal complex space is introduced for representation of the quark flavors. Quark masses are generalized to operators operating on functions in this space. A simple model is proposed for the meson internal functions and mass operators producing the squares of the average quark masses as eigenvalues. The present space-time model calls for a particle classification scheme different from the usual nonrelativistic one. When combined with the internal model, it may account for the gross structure of the meson spectra together with the form of an empirical relation. Upper limits of bare quark masses are estimated from simplified analytical solutions of the radial equations and agree approximately with the bare quark masses obtained from baryon data in a companion paper. The radial equations are solved numerically yielding estimates of the strong interaction radii of the ground state mesons.     

Dilepton production in proton-nucleus and nucleus-nucleus collisions at SPS energies

Dilepton production in proton- and nucleus-induced reactions is studied in the relativistic transport model using initial conditions determined by the string dynamics from RQMD. It is found that both the CERES and HELIOS-3 data for dilepton spectra in proton-nucleus reactions can be well described by the ‘conventional’ mechanism of Dalitz decay and direct vector meson decay. However, to provide a quantitative explanation of the observed dilepton spectra in central S+Au and S+W collisions requires contributions other than these direct decays. Introducing a decrease of vector meson masses in hot and dense medium, we find that these heavy-ion data can also be satisfactorily explained. This agrees with our earlier conclusions based on a fire-cylinder model. We also give predictions for Pb+Au collisions at 160 GeV/nucleon using current CERES mass resolution and acceptance.     

Low mass dimuons produced in relativistic nuclear collisions

The NA60 experiment has measured low mass muon pair production in In-In collisions at 158A GeV with unprecedented precision. We show that these data are reproduced very well by a dynamical model with parameters scaled from fits to measurements of hadronic transverse mass spectra and Hanbury Brown-Twiss correlations in Pb-Pb and Pb-Au collisions at the same energy. The data are consistent with in-medium properties of rho and omega mesons at finite temperature and density as deduced from empirical forward-scattering amplitudes. Inclusion of the vacuum decay of the rho meson after freeze-out is necessary for an understanding of the mass and transverse momentum spectrum of dimuons with M less similar 0.9 GeV/c(2).     

瞬时相互作用近似下介子结构波函数的一些探讨(Ⅰ)——瞬时相互作用下介子波函数的一般性质

本文从一对正反费米子结合成束缚态的Bethe-Salpeter方程(以下简称B-S方程)出发,假定正反层子间相互作用可以近似地用质心系瞬时相互作用描写,得到的主要结论如下:(1)B-S方程的求解可归结为在质心系三维空间内进行。描写赝标介子和矢量介子的波函数独立旋量分量的个数分别由4个和8个减少为2个和4个;(2)如果相互作用是空间球对称的,其旋量结构是对角耦合,从赝标介子方程中可以直接看到,束缚态质量作为本征值在方程中是以平方形式出现,同时又可避免四维方程中负激发的困难;(3)在瞬时相互作用近似下给出的结构波函数,可以用来研究束缚态的质量谱和只涉及质心系的过程。     

夸克和弦模型中非奇异轻介子的类雷吉谱(英文)

本工作重新考察了相对论弦模型和准相对论夸克模型中轻介子的类雷吉谱。基于辅助场技术,提出了非奇异轻介子的一个解析质量公式,由此推导出了一个准线性的Regge-Chew-Frautschi轨迹关系,并将此关系用相应介子的实验数据（PDG）进行了检验。检验结果表明,和实验观测数据比较,夸克模型对介子质量的预言与弦模型的相符,但在角动量较大时,夸克模型的预言稍微优于弦模型。We revisit the Regge-like spectra of light mesons in the relativistic string model and the simirelativistic quark model. An analytical mass formula is proposed for light mesons based on the auxiliary field technique, and a quasi-linear Regge-Chew-Frautschi plot with flavor dependence is derived and verified with the experimental data(PDG) for light mesons.The results show that the quark model predictions for meson masses agree with those of the string model, but are slightly better when the angular momentum is relatively large as compared with the observed data.     

Broadening of ρ(→ e+e−) meson produced coherently in the photonuclear reaction

The e ⁺ e ^? invariant mass distribution spectra are calculated to estimate the hadron parameters of the ρ meson produced coherently in the photonuclear reaction. The elementary reaction occurring in the nucleus is considered to proceed as γN → ρ ⁰ N; ρ ⁰ → e ⁺ e ^?. We describe the elementary ρ meson photoproduction by the experimentally determined reaction amplitude $f_{\gamma {\rm N} \to \rho ^0 {\rm N}}$ . The ρ meson propagator is presented by the eikonal form, and the ρ meson nucleus optical potential V _Oρ appearing in it is estimated using the “t?” approximation. The ρ meson nucleon scattering amplitude f _ρN extracted from the measurements is used to generate this potential. The calculated e ⁺ e ^? invariant mass distribution spectra are compared with those measured at Jefferson Laboratory. The calculated results for the transparency ratio are also presented.