arXiv subjects
Publications and source records attributed to Cheuk-Yin Wong.
The combined considerations of both the bulk liquid-drop-type behawior and the quantized angular momentum reveal that high-spin toroidal isomeric states may have general occurrences for light nuclei with 28 <= A <= 48. High-spin N=Z toroidal isomers in this mass region have been located theoretically using cranked self-consistent constraint Skyrme-Hartree-Fock model calculations.
The electron and the positron treated as point particles in the Two Body Dirac equations of constraint dynamics for QED possess a new and as yet undiscovered peculiar ${}^1S_0$ bound-state which has a very large binding energy of about 300 keV, in addition to the usual ${}^1S_0$ positronium state with a binding energy of 6.8 eV. The production and detection of the peculiar ${}^1S_0$ state provide a test of the electron point-charge property. As the peculiar ${}^1S_0$ state lies lower than the usual ${}^1S_0$ state, the peculiar ${}^1S_0$ state can be produced by a two-photon decay of the usual $^{1}S_{0}$ state. We estimate the rate of the two-photon decay and show how it depends on the probability $P_{up}$ of the admixture of the peculiar component in the predominantly usual ${}^1S_0$ positronium. The produced peculiar ${}^1S_0$ state in turn annihilates into two photons with a total c.m. energy of about 723 keV. Thus the signature for this new peculiar ${}^1S_0$ positronium bound state would be the decay of the usual ${}^1S_0$ state into four photons, with two energies bunching around 150 and two around 360 keV. Such a four-photon decay of the usual ${}^1S_0$ state will not be present if the electron and positron are not point particles, or if the mixing probability $P_{up}$ is very small.
Previous analytical formulas in the Glauber model for high-energy nucleus-nucleus collisions developed by Wong are utilized and extended to study antiproton-nucleus annihilations for both high and low energies, after taking into account the effects of Coulomb and nuclear interactions, and the change of the antiproton momentum inside a nucleus. The extended analytical formulas capture the main features of the experimental antiproton-nucleus annihilation cross sections for all energies and mass numbers. At high antiproton energies, they exhibit the granular property for the lightest nuclei and the black-disk limit for the heavy nuclei. At low antiproton energies, they display the effect of the antiproton momentum increase due to the nuclear interaction for the light nuclei, and the effect of the magnification due to the attractive Coulomb interaction for the heavy nuclei.
Hydrodynamics and quantum mechanics have many elements in common, as the density field and velocity fields are common variables that can be constructed in both descriptions. Starting with the Schroedinger equation and the Klein-Gordon for a single particle in hydrodynamical form, we examine the basic assumptions under which a quantum system of particles interacting through their mean fields can be described by hydrodynamics.
Productions of soft photon with low transverse momenta in high-energy hadron-hadron collisions and $e^+$-$e^-$ annihilations indicate that they are consistently produced in excess of what are predicted by electromagnetic bremsstrahlung when hadrons (mostly mesons) are produced, but they agree with electromagnetic bremsstrahlung predictions in the absence of hadron production. These excess soft photons are called anomalous soft photons. The occurrence of anomalous soft photons in association with hadron production reveals the presence of additional QED soft photon sources in QCD hadron production. Many different models have been proposed to explain the anomalous soft production. We shall examine specifically a quantum field theory of simultaneous meson and soft photon production in QCDxQED in which the meson production arises from the oscillation of color charge densities of the quarks of the underlying vacuum in a flux tube. As a quark carries both a color charge and an electric charge, the oscillation of the color charge densities will be accompanied by the oscillation of electric charge densities, which will in turn lead to the simultaneous production of anomalous soft photons during the meson production process.
We review recent applications of the Two Body Dirac equations of constraint dynamics to meson spectroscopy and describe new extensions to three-body problems in their use in the study of baryon spectroscopy. We outline unique aspects of these equations for QED bound states that distinguish them among the various other approaches to the relativistic two body problem. Finally we discuss recent theorectial solutions of new peculiar bound states for positronium arising from the Two Body Dirac equations of constraint dynamics, assuming point particles for the electron and the positron.
Using one- and two-body density matrices, we calculate the spatial and momentum distributions, two-particle Hanbury-Brown Twiss (HBT) correlation functions, and the chaotic parameter $λ$ in HBT interferometry for the systems of boson gas within the harmonic oscillator potentials with anisotropic frequencies in transverse and longitudinal directions. The HBT chaotic parameter, which can be obtained by measuring the correlation functions at zero relative momentum of the particle pair, is related to the degree of Bose-Einstein condensation and thus the system environment. We investigate the effects of system temperature, particle number, and the average momentum of the particle pair on the chaotic parameter. The value of $λ$ decreases with the condensed fraction, $f_0$. It is one for $f_0=0$ and zero for $f_0=1$. For a certain $f_0$ between 0 and 1, we find that $λ$ increases with the average momentum of the particle pair and decreases with the particle number of system. The results of $λ$ are sensitive to the ratio, $ν=ω_z/ω_ρ$, of the frequencies in longitudinal and transverse directions. They are smaller for larger $ν$ when $ω_ρ$ is fixed. In the heavy ion collisions at the Large Hadron Collider (LHC) energy the large identical pion multiplicity may possibly lead to a considerable Bose-Einstein condensation. Its effect on the chaotic parameter in two-pion interferometry is worth considering in earnest.
Motivated by the good Tsallis fits to the high-pT spectra in pp collisions at the LHC, we study the relativistic hard-scattering model and obtain an approximate analytical expression for the differential hard-scattering cross section at η~ 0. The power-law behaviour of the transverse spectra, in the form of dσ/dpT^2 \propto 1/pT^n, gives a power index n in the range of 4.5-5.5 for jet production as predicted by pQCD, after the dependencies of the structure functions and the running coupling constant are properly taken into account. The power indices for hadron production n are slightly greater than those for jet production.
Phenomenological Tsallis fits to the CMS, ATLAS, and ALICE transverse momentum spectra of hadrons for pp collisions at LHC were recently found to extend over a large range of the transverse momentum. We investigate whether the few degrees of freedom in the Tsallis parametrization may arise from the relativistic parton-parton hard-scattering and related processes. The effects of the multiple hard-scattering and parton showering processes on the power law are discussed. We find empirically that whereas the transverse spectra of both hadrons and jets exhibit power-law behavior of 1/pT^n at high pT, the power indices n for hadrons are systematically greater than those for jets, for which n~4-5.
We show from the action integral that in the special environment of a flux tube, QCD$_4$ in (3+1) dimensional space-time can be approximately compactified into QCD$_2$ in (1+1) dimensional space-time. In such a process, we find out how the coupling constant $g_{2D}$ in QCD$_2$ is related to the coupling constant $g_{4D}$ in QCD$_4$. We show how the quark and the gluon in QCD$_2$ acquire contributions to their masses arising from their confinement within the tube, and how all these quantities depend on the excitation of the partons in the transverse degrees of freedom. The compactification facilitates the investigation of some dynamical problems in QCD$_4$ in the simpler dynamics of QCD$_2$ where the variation of the gluon fields leads to a bound state.
Previously a compact formula for total reaction cross section for heavy-ion collisions as a function of energy was obtained by treating the angular momentum $l$ as a continuous variable. The accuracy of the continuum approximation is assessed and corrections are evaluated. The accuracy of the compact equation can be improved by a simple modification, if a higher accuracy is required. Simple rules to determine the barrier heights and the penetration probability for the $l$ partial wave from experimental data are presented, for the collision of identical or non-identical light nuclei.
Phenomenological Tsallis fits to the CMS and ATLAS transverse spectra of charged particles were found to extend for p_T from 0.5 to 181 GeV in pp collisions at LHC at \sqrt{s}=7 TeV, and for p_T from 0.5 to 31 GeV at \sqrt{s}=0.9 TeV. The simplicity of the Tsallis parametrization and the large range of the fitting transverse momentum raise questions on the physical meaning of the degrees of freedom that enter into the Tsallis distribution or q-statistics.
In the Feynman amplitude approach for coherent collisions of a jet with medium partons, the Bose-Einstein symmetry with respect to the interchange of the exchanged bosons leads to a destructive interference of the amplitudes in most regions of the phase space but a constructive interference in some other regions. As a consequence, there is a collective longitudinal momentum transfer to the scatterers along the jet direction, each scatterer carrying a substantial fraction of the incident jet longitudinal momentum. The manifestation of the Bose-Einstein interference may have been observed in angular correlations of hadrons associated with a high-p_T trigger in high-energy collisions at RHIC and LHC.
We show from the action integral that under the assumption of longitudinal dominance and transverse confinement, QCD4 in (3+1) dimensional space-time can be approximately compactified into QCD2 in (1+1) dimensional space-time. In such a process, we find the relation between the coupling constant g(2D) in QCD2 and the coupling constant $g(4D)$ in QCD4. We also show that quarks and gluons in QCD2 acquire masses as a result of the compactification.
The magnetic interactions between a fermion and an antifermion of opposite electric or color charges in the 1S0 and 3P0 states are very attractive and singular near the origin and may allow the formation of new bound and resonance states at short distances. In the two body Dirac equations formulated in constraint dynamics, the short-distance attraction for these states for point particles leads to a quasipotential that behaves near the origin as -α^2/r^2. Both 1S0 and 3P0 states admit two types of eigenstates with drastically different behaviors for the radial wave function u=rψ. One type of states, with u growing as r^{1+\sqrt(1-4*α^2)/2} at small r, will be called usual states. The other type of states with u growing as r^{(1-\sqrt(1-4*α^2))/2} will be called peculiar states. Both of the usual and peculiar eigenstates have admissible behaviors at short distances. The usual bound 1S0 states possess attributes the same as those one usually encounters in QED and QCD. In contrast, the peculiar bound 1S0 states, yet to be observed, have distinctly different bound state properties and scattering phase shifts. For the 3P0 states, the usual solutions lead to the standard bound state energies and no resonance, but resonances have been found for the peculiar states whose energies depend on the description of the internal structure of the charges, the mass of the constituent, and the coupling constant. The existence of both usual and peculiar eigenstates in the same system leads to the non-self-adjoint property of the mass operator and two non-orthogonal complete sets. The mass operator can be made self-adjoint with a single complete set of admissible states by introducing a new peculiarity quantum number and an enlarged Hilbert space.
When a jet collides coherently with many parton scatterers at very high energies, the Bose-Einstein symmetry with respect to the interchange of the virtual bosons leads to a destructive interference of the Feynman amplitudes in most regions of the momentum transfer phase space but a constructive interference in some other regions of the momentum transfer phase space. As a consequence, the recoiling scatterers have a tendency to come out collectively along the incident jet direction, each carrying a substantial fraction of the incident jet longitudinal momentum. The manifestation of the Bose-Einstein interference as collective recoils of the scatterers along the jet direction may have been observed in angular correlations of hadrons associated with a high-pT trigger in high-energy heavy-nuclei collisions at RHIC and LHC.
When an energetic particle collides coherently with many medium particles at high energies, the Bose-Einstein symmetry with respect to the interchange of the exchanged virtual bosons leads to a destructive interference of the Feynman amplitudes in most regions of the phase space but a constructive interference in some other regions of the phase space. As a consequence, the recoiling medium particles have a tendency to come out collectively along the direction of the incident fast particle, each carrying a substantial fraction of the incident longitudinal momentum. Such an interference appearing as collective recoils of scatterers along the incident particle direction may have been observed in angular correlations of hadrons associated with a high-$p_T$ trigger in high-energy AuAu collisions at RHIC.
The big mass difference between the pion and rho meson possibly originates from the spin-dependent nature of the interactions in the two states since these two states are similar except for spin. Both pi and rho are quark-antiquark systems which can be treated using the two-body Dirac equations (TBDE) of constraint dynamics. This relativistic approach for two-body system has the advantage over the non-relativistic treatment in the sense that the spin-dependent nature is automatically coming out from the formalism. We employed Dirac's relativistic constraint dynamics to describe quark-antiquark systems. Within this formalism, the 16-component Dirac equation is reduced to the 4-component 2nd-order differential equation and the radial part of this equation is simply a Schroedinger-type equation with various terms calculated from the basic radial potential. We used a modified Richardson potential for quark-antiquark systems which satisfies the conditions of confinement and asymptotic freedom. We obtained the wave functions for these two mesons which are not singular at short distances. We also found that the cancellation between the Darwin and spin-spin interaction terms occurs in the pi mass but not in the rho mass and this is the main source of the big difference in the two meson masses.