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。     

介子结构中的一种可能位势

本文在层子模型的基础上,应用B-S方程讨论了介子结构。结果指出,如果引入深底方位阱、谐振势和库仑型势的迭加位势,用于讨论介子束缚态时,能初步解释介子的能谱、平均半径与原点波函数等特性。     

重味展开下的0~－重介子束缚态

用瞬时近似下的Ｂｅｔｈｅ－Ｓａｌｐｅｔｅｒ（Ｂ－Ｓ）方程，讨论了０－重介子束缚态．运用重味质量展开方法求解方程，计算了一级近似下Ｄ±，Ｄ０，Ｂ±，Ｂ０介子的质量，与实验数据和其它求解方法的计算结果作了比较．     

介子束缚态方程及其解的进一步探讨

在资料[1]讨论过的一种可能的介子束缚态方程的基础上,着重在位阱形状参量v值较大（v=10²～10³）的情形下,对方程的解作了进一步的探讨.结果指出,特征值λ和有关物理量对位阱参量v、E的依赖关系大致仍有资料[1]所述的规律性,但介子束缚态平均半径的数值当v较大时,并不随v的继续增大而不断增加.对应于每一个参量v值,存在一个最大的介子平均半径,当v>10²时,所有的约为12.6M^-1（M为层子质量）,尚小于π介子的物理半径.若考虑到层子与反层子之间的超强相互作用除这种吸引势外还存在另一排斥势,并引入和资料[1]中位势V_v（r）相应的差型V_v（r）势进行计算,可使介子束缚态半径与实验值接近的程度有较大改进.     

重味展开下的0－重介子束缚态

用瞬时近似下的Bethe-Salpeter(B-S)方程,讨论了0^－重介子束缚态.运用重味质量展开方法求解方程,计算了一级近似下D^±,D⁰,B^±,B⁰介子的质量,与实验数据和其它求解方法的计算结果作了比较.     

双环形Hulthén势束缚态的近似解析解

构造了双环形Hulthén势, 用指数函数近似表示任意分波的离心项, 运用函数分析法讨论双环型Hulthén势Schrödinger方程的束缚态解. 归一化的角向波函数和径向波函数用超几何多项式表示, 给出了束缚态能谱, 体系的束缚态的能谱方程和波函数与量子数和势参数有关. 中心势场和单环形势场角向波函数及 Hulthén势束缚态能谱是本文双环形Hulthén势的特例. 关键词： 双环形Hulthén势 任意分波 近似解析解 束缚态     

∑-N相互作用的介子交换势

本文用文献[1]的方法从介子交换观点讨论了三超子与核子的相互作用,利用单玻色子交换(OBEP)和双玻色子交换(TBEP)两种机制,在低能近似下,得到一个Σ-N相互作用势.计算表明只有同位旋I=3/2,自旋S=0的Σ-N系统有可能存在束缚态.     

任意维l态Woods-Saxon势的精确解

在D维空间下使用完全量子化规则计算了具有离心项的Woods-Saxon势,根据动量积分 (其中 )和Pekeris近似化条件,得到了系统的任意l波Schrödinger方程的解和能谱方程．讨论了束缚态能谱的有关性质．     

任意维l态Woods-Saxon势的精确解

在D维空间下使用完全量子化规则计算了具有离心项的Woods-Saxon势,根据动量积分 (其中 )和Pekeris近似化条件,得到了系统的任意l波Schrödinger方程的解和能谱方程．讨论了束缚态能谱的有关性质．     

瞬时相互作用近似下介子结构波函数的一些探讨(Ⅱ) 赝标介子和矢量介子的谐振子模型

本文在文献[1]基础上讨论由一对正反层子组成的介子结构波函数。假定层子质量很重,相互作用是谐振子位阱,旋量耦合方式符合一定的要求,则可以普遍给出以下结果:(1)自动给出质量谱的平方等距关系,又可以避免通常谐振子基态能级过高的困难;(2)如果层子原始弱流为V-A型,层子原始电磁流无反常磁矩项,可以解决赝标介子二体轻子衰变Cabibbo角的不谐调和矢量介子衰变到e~ e~-几率比的困难;(3)只要在相互作用中引入很小比例的SU(3)破坏项,就足以解释现有介子质量的SU(3)分裂。这就对为什么K-π质量差3.5倍却在许多情况下表现有相当好的SU(3)对称性给以一个合理解释;(4)方程的展开和波函数都有较好的近似性;(5)介子中层子反层子分布半径与现有关于介子电磁半径的实验量级是可以谐调的;(6)介子结构波函数的旋量结构和动量结构都是完全确定的。     

THE WAVE FUNCTION OF VECTOR MESON BOUND STATE THROUGH SCALAR COUPLING

The wave function of the vector bound state of a spinor straton-antistraton pair through scalar coupling is discussed.The Bethe-Salpeter equation of the bound state is solved numerically,and the structural wave functions of the vector bound state are given corresponding to different selection of the parametcrs of the kernel. The magnitude of various invariant functions of the wave function is determined. The validity of the Bargman-Wigner approximation is also examined.     

WHAT IS THE NATURE OF THE NEWLY DISCOVERED HEAVY PARTICLE γ(9.5)

In this paper, we discuss the nature of the newly discovered heavy particle Y（9.5）. Five possibilities of experimental criteria are analysed. We show that if Y is a heavy photon, an intermediate boson, a bound state of straton-antistraton or a hadron without valence stratons, and all the Γee will differ by several orders of magnitude and can therefore be discriminated easily in e⁺ e^-collision experiments. The width value Fee and its ratio of γ to γ' are not identical for the case of colour excited states of meson and the case of bound states of the new straton-antistraton. The masses of other existing new particles can also be predicted. In particular, the masses of weakly decaying heavy particles are not the same for these two cases, which may be regarded as a criterion to discriminate between these two cases. We have also discussed the main decaying properties of γ for these five possibilities.     

Observation of exotic meson production in the reaction pi- p --> eta'pi- p at 18 GeV/c

An amplitude analysis of an exclusive sample of 5765 events from the reaction pi- p-->eta'pi- p at 18 GeV/c is described. The eta'pi- production is dominated by natural parity exchange and by three partial waves: those with J(PC) = 1(-+), 2(++), and 4(++). A mass-dependent analysis of the partial-wave amplitudes indicates the production of the a2(1320) meson as well as the a4(2040) meson, observed for the first time decaying to eta'pi-. The dominant, exotic (non- qq) 1(-+) partial wave is shown to be resonant with a mass of 1.597+/-0.010(+0.045)(-0.010) GeV/c2 and a width of 0.340+/-0.040+/-0.050 GeV/c2. This exotic state, the pi1(1600), is produced with a t dependence which is different from that of the a2(1320) meson, indicating differences between the production mechanisms for the two states.     

Guided waves in elastic rectangular bars:A solution using partial plate mode decomposition

Similar to Auld's solution for Lamb waves,the wave modes in elastic rectangular bar are solved by partial wave decomposition method.The partial waves are composed of plate modes with the same wavenumber component in waveguide longitudinal direction,thus free boundary conditions on one pair of opposite surfaces are automatically satisfied.Based on completeness assumption and orthogonality of the plate modes,four independent eigenequations are eventually derived for dispersion curve and mode shape investigation.Numerical evaluation shows the calculated results are in consistent with the FEM results.It is then verified that the plate modes which obliquely bounced back and forth between the two opposite surfaces compose the guided modes traveling in the rectangular waveguides with certain wave numbers in transversely resonant cases.     

Perturbative QCD study on the photonic penguin contributions to the decay B\rightarrow K^* \gamma

Including corrections of order , we present an analysis of photonic penguin contributions to the decay in the perturbative QCD framework. Employing several models of the meson wave functions, we demonstrate that the corrections of are enhanced and will provide substantial contributions to the decay because of the meson wave function being sharply peaked (bound state effect). The numerical predictions for the corrections are about which depend on the non-perturbative inputs such as the meson wave functions and the -quark mass. Received: 8 July 1997 / Published online: 23 February 1998     

矩形截面固体波导中弹性导波模式的板波叠加解

参照板中兰姆波模式的子波叠加解求解了矩形截面固体波导中弹性导波的模式。其中子波设定为横向满足自由边界反射条件、纵向波数分量相同的各板波模式。假设声场的完备性,利用子波模式的正交性,结合矩形截面的几何对称性可以得到4组独立导波特征方程用于频散曲线以及导波模式计算,其计算结果与有限元法计算结果相符。研究以解析模型表明:矩形截面固体波导中的导波是其内部以一定纵向波数分量斜向传播的板波模式在两个自由侧面上经过反复反射与模式转化后,横向耦合谐振而形成的。      

Bifurcation,stability and symmetry of nonlinear waves

The bifurcation of wave-like spatio-temporal structures due to a hard-mode instability at non-zero wave number is investigated for a simple class of driven systems in one space dimension. We find generically a bifurcation of two branches of waves, travelling waves and standing waves, characterized by nontrivial subgroups of the symmetry group of the system. If both branches are supercritical, the wave with the larger amplitude is found to be stable. In all other cases, both waves are unstable for small amplitudes. At the common boundary of the stability regions of the two wave types in parameter space we find a bifurcation of a branch of modulated waves involving two independent frequencies, connecting the branches of travelling waves and standing waves.Work supported by the Swiss National Science Foundation     

Few-Body Aspects of the Near Threshold Pseudoscalar Meson Production

During the last decade large samples of data have been collected on the production of the ground-state pseudoscalar mesons in collisions of proton or deuteron beam with hydrogen or deuterium target. These measurements have been performed in the vicinity of the kinematical threshold for meson production where only a few partial waves in both initial and final state are expected to contribute to the production process. This simplifies significantly the interpretation of the data, yet still appears to be challenging due to the three or four particle final state systems with a complex hadronic potential. We review experiments and phenomenology of the near threshold production of the ground-state mesons in the few-body final states as for example: nucleus-meson and nucleon-nucleon-meson, and report on the status of the search of the mesic-nuclei (a meson-nucleus bound states). Experimental advantages of measurements close to the kinematical threshold are discussed, and general features of the production mechanism of the η and η′ mesons in the nucleon-nucleon collisions are presented emphasising results of measurements of spin and isospin dependence of the production cross sections.