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Central collisions in intermediate energy heavy-ion reactions. [Micro- and macroscopic theory, extended time-dependent Hartree-Fock approximation]

Description: The critical collisions in intermediate energy heavy-ion reactions are examined from both a microscopic and macroscopic viewpoint. In the microscopic description the proper tool is the extended TDHF approximation involving both the mean field and the particle collisions. To understand the underlying physics, the effect of the mean field and the effect of particle collisions are studied separately. It is found that th sudden increase in the density of the overlapping region can cause the volcano effect, leading to the complete disintegration of one of the nuclei. The self-consistent mean field also gives rise to the bunching instability when the two Fermi spheres of the colliding nucleons separate. The collision between nucleons, on the other hand, leads to irreversible dissipation, thermalization, and the possibility of a hydrodynamical description of the dynamics. Next is studied the dynamics of central collisions using the hydrodynamical description for many combinations of targets and projectiles at different energies. The formation of shock waves, sidesplash, and the complete disintegration of the whole nucleus are examined. Nuclear viscosity is found to affect the angular distribution of the reaction products and also the maximum compression ratio achieved during the collision. 28 references.
Date: January 1, 1979
Creator: Wong, C.Y.
Partner: UNT Libraries Government Documents Department

Classical transcription of the TDHF approximation

Description: The time-dependent Hartree--Fock approximation is shown to be approximately equivalent to a purely classical pseudoparticle simulation. In this simulation, a collection of pseudoparticles are introduced to discretize the phase space of spatial and momentum coordinates. The dynamics is completely determined by following the pseudoparticle trajectories which are the same as the trajectories of real particles moving in the self-consistent field. An application of these concepts to nearly-head-on heavy-ion collisions leads to a better understanding of the origin of the low-l fusion window obtained in the TDHF calculations. 1 table.
Date: January 1, 1979
Creator: Wong, C.Y.
Partner: UNT Libraries Government Documents Department

Extended TDHF approximation illuminates the approach to thermal equilibrium

Description: The region of validity of the TDHF approximation is extended by including the collisions between particles. The resultant equations of motion consist of a modified TDHF equation and a master equation for the occupation numbers. Concepts such as entropy, temperature, and thermal equilibrium can be quantitatively introduced. The well-known H-theorem that entropy never decreases is proved for nuclear systems. New types of level crossing formulas are obtained to shed light on how a nonequilibrium finite nuclear system approaches thermal equilibrium. 2 figures.
Date: January 1, 1979
Creator: Wong, C.Y. & Tang, H.H.K.
Partner: UNT Libraries Government Documents Department

Nuclear momentum distribution and relativistic heavy-ion reactions

Description: In terms of a direction fragmentation process and a hard-scattering process, the proton-inclusive data for the reaction ..cap alpha.. + /sup 12/C ..-->.. p + X were successfully analyzed. The extracted semiempirical momentum distribution indicates possible evidence of nuclear correlations and final-state interactions. 4 figures.
Date: January 1, 1980
Creator: Wong, C.Y. & Blankenbecler, R.
Partner: UNT Libraries Government Documents Department

Scaling phenomenon in relativistic nucleus-nucleus collisions

Description: New scaling variables for proton and pion production in relativistic nucleus-nucleus collisions are introduced which are the generalizations of the Feynmann scaling variable. They allow a simple description of the cross sections at forward and backward angles. 2 figures.
Date: January 1, 1980
Creator: Wong, C.Y. & Blankenbecler, R.
Partner: UNT Libraries Government Documents Department

Incorporation of particle collisions in the time-dependent Hartree-Fock approximation

Description: In the time-dependent Hartree-Fock (TDHF) approximation, particles interact only through the mean field, and the collisions between particles are not included. Previously, we formulated the extended time-dependent Hartree-Fock (ETDHF) approximation to include particle collisions in terms of a temporal variation of the occupation probability n/sub lambda/ for the single-particle states. In the simplest approximation, the single-particle potential is modified only through the particle density which depends on n/sub lambda/. We wish to refine the extended TDHF approximation by studying how particle collisions affect the single-particle potential. We find that it acquires two second-order contributions which are state-dependent and are the generalization of the core polarization and correlation contributions one encounters in the study of the nucleon-nucleus optical potentials. In consequence, concepts such as energy-dependent single-particle potentials and effective masses may be properly introduced in the extended TDHF approximation. We also wish to review the conservation of energy in the ETDHF approximation. We find that the total energy should include a second-order contribution due to correlations arising from particle collisions.
Date: January 1, 1982
Creator: Wong, C.Y.
Partner: UNT Libraries Government Documents Department

Viscoelastic properties of the nucleus

Description: The Maxwell solid, which has a short-time elastic behavior and a long-time viscous behavior, cannot properly describe the viscoelastic properties of the nuclear fluid in its ground state. The Voigt solid, which exhibits asymptotically an elastic behavior, is a good model for the nuclear fluid in its ground state.
Date: January 1, 1982
Creator: Wong, C.Y. & Azziz, N.
Partner: UNT Libraries Government Documents Department

Baryon distribution in relativistic heavy-ion collisions

Description: Recently there has been considerable interest in highly relativistic heavy-ion collisions which was suggested as a way to produce a phase transition from the ordinary confined matter to the unconfined quark-gluon plasma. As the fraction of baryons in the early universe was small, it seems desirable to design a heavy-ion collider such that when the energy density in the central rapidity is high enough for a phase transition, there is no net baryon density there. Recent investigations reveal that the average downward shift of the projectile baryon rapidity is quite large. The formation of a pure quark-gluon plasma depends on the shape of the baryon momentum distributions. It is of interest to estimate the baryon momentum distribution. We shall study the baryon distribution using the Glauber-type multiple collision model. In this model, a nucleon in one nucleus makes many inelastic collisions with nucleons in the other nucleus, the probability being given by the thickness function and the total nucleon-nucleon inelastic cross section. Each baryon-baryon collision results in a degradation of their energies and momenta in accordance with experimental nucleon-nucleon inelastic differential cross section data. This model is an extension of the model of Blankenbecler et al. to include the effect of energy degradation. We shall focus our attention on the longitudinal momentum distribution in terms of the Feynman scaling variable x.
Date: January 1, 1984
Creator: Wong, C.Y.
Partner: UNT Libraries Government Documents Department

Initial energy density of quark-gluon plasma in relativistic heavy-ion collisions

Description: Recently, there has been considerable interest in the central rapidity region of highly relativistic heavy-ion collisions. Such an interest stems from the possibility of creating hadron matter of high energy density which may exceed the critical energy density for a phase transition between ordinary confined matter and the unconfined quark-gluon plasma. The experimental searches and identification of the quark-gluon plasma may provide a new insight into the question of quark confinement. The estimate of the initial energy density is quite uncertain. The initial energy density is nonetheless an important physical quantity. It is one of the factors which determines whether the produced matter can undergo phase transition or not. The energy density has been estimated previously by using the color neutralization model of Brodsky et al. However, the color neutralization model gives a central rapidity multiplicity in heavy-ion collision too low by a factor of two. For this reason, we wish to obtain a better estimate of the energy density (in the central rapidity region). As is well known, a simple Glauber-type multiple collision model can reproduce the total multiplicity and multiplicity plateau near the central rapidity region to within 30%. The simple multiple collision model has an approximate validity as a gross description of the reaction process. We shall adopt a semiempirical approach. Using the multiple collision model and the thickness function of Glauber, we obtain analytical functional form for all the quantities in question. A single parameter, r/sub rms/, is adjusted to fit the experimental central rapidity multiplicity data. The semi-empirical results provide a useful tool to extrapolate to the unknown central rapidity region of heavy-ion collisions.
Date: January 1, 1984
Creator: Wong, C.Y.
Partner: UNT Libraries Government Documents Department

A detailed study of nonperturbative solutions of two-body Dirac equations

Description: In quark model calculations of the meson spectrums fully covariant two-body Dirac equations dictated by Dirac's relativistic constraint mechanics gave a good fit to the entire meson mass spectrum for light quark mesons as well as heavy quark mesons with constituent world scalar and vector potentials depending on just one or two parameters. In this paper, we investigate the properties of these equations that made them work so well by solving them numerically for quantum electrodynamics (QED) and related field theories. The constraint formalism generates a relativistic quantum mechanics defined by two coupled Dirac equations on a sixteen component wave function which contain Lorentz covariant constituent potentials that are initially undetermined. An exact Pauli reduction leads to a second order relativistic Schroedinger-like equation for a reduced eight component wave function determined by an effective interaction -- the quasipotential. We first determine perturbatively to lowest order the relativistic quasipotential for the Schroedinger-like equation by comparing that form with one derived from the Bethe-Salpeter equation. Insertion of this perturbative information into the minimal interaction structures of the two-body Dirac equations then completely determines their interaction structures. Then we give a procedure for constructing the full sixteen component solution to our coupled first-order Dirac equations from a solution of the second order equation for the reduced wave function. Next, we show that a perturbative treatment of these equations yields the standard spectral results for QED and related interactions.
Date: December 1, 1992
Creator: Crater, H.W.; Becker, R.L.; Wong, C.Y. & Van Alstine, P.
Partner: UNT Libraries Government Documents Department

A detailed study of nonperturbative solutions of two-body Dirac equations

Description: In quark model calculations of the meson spectrums fully covariant two-body Dirac equations dictated by Dirac`s relativistic constraint mechanics gave a good fit to the entire meson mass spectrum for light quark mesons as well as heavy quark mesons with constituent world scalar and vector potentials depending on just one or two parameters. In this paper, we investigate the properties of these equations that made them work so well by solving them numerically for quantum electrodynamics (QED) and related field theories. The constraint formalism generates a relativistic quantum mechanics defined by two coupled Dirac equations on a sixteen component wave function which contain Lorentz covariant constituent potentials that are initially undetermined. An exact Pauli reduction leads to a second order relativistic Schroedinger-like equation for a reduced eight component wave function determined by an effective interaction -- the quasipotential. We first determine perturbatively to lowest order the relativistic quasipotential for the Schroedinger-like equation by comparing that form with one derived from the Bethe-Salpeter equation. Insertion of this perturbative information into the minimal interaction structures of the two-body Dirac equations then completely determines their interaction structures. Then we give a procedure for constructing the full sixteen component solution to our coupled first-order Dirac equations from a solution of the second order equation for the reduced wave function. Next, we show that a perturbative treatment of these equations yields the standard spectral results for QED and related interactions.
Date: December 1, 1992
Creator: Crater, H. W.; Becker, R. L.; Wong, C. Y. & Van Alstine, P.
Partner: UNT Libraries Government Documents Department

J/{Psi} suppression as a signal for the quark-gluon plasma

Description: The authors review the search for the quark-gluon plasma using the signal of the suppression of J/{psi} production in high-energy heavy-ion collisions. Recent anomalous J/{psi} suppression in high-energy Pb-Pb collisions observed by the NA50 Collaboration are examined and compared with earlier results from pA and nucleus-nucleus collisions with heavy ions of smaller mass numbers. The anomalous suppression of J/{psi} production in Pb-Pb collisions can be explained as due to the occurrence of a new phase of strong J/{psi} absorption, which sets in when the number of nucleon-nucleon collisions at a spatial point exceeds about 4 and corresponds to a local energy density of about 3.4 GeV/fm{sup 3}.
Date: December 1, 1997
Creator: Wong, C.Y.
Partner: UNT Libraries Government Documents Department

Heavy quarkonium production and propagation in nuclei

Description: In the search for the quark-gluon plasma, it has been suggested that the production of charmonium will be suppressed in a quark-gluon plasma because of the screening of the interaction between c and {anti c}. To extract information on the suppression due to the quark-gluon plasma, it is necessary to study the suppression of J/{psi} production by sources different from the quark-gluon plasma. It is therefore useful to examine the mechanism of heavy quarkonium production and its propagation in nuclei. The authors describe a precursor in heavy quarkonium production in terms of a coherent admixture of states of different color, spin, and angular momentum quantum numbers, and obtain the production amplitudes for different quarkonium bound states by projecting out this precursor state onto these bound states. The precursor is absorbed in its passage through a nucleus in a pA reaction, and the total cross section between this precursor with a nucleon can be calculated with the two-gluon model of the Pomeron. Such a description of coherent precursors and their subsequent interactions with nucleons can explain many salient features of J/{psi} and {psi}{prime} production in pA collisions.
Date: December 31, 1997
Creator: Wong, C.Y.
Partner: UNT Libraries Government Documents Department

Possible mechanism of formation and stability of anomalous states of water

Description: The authors examine the physical processes which are involved in the formation and stability of the anomalous states of water reported recently. The initial step of adding a small amount of ionic compound X{sup +}Y{sup {minus}} to pure water leads t the formation of water clusters X{sup +} (H{sub 2}O){sub n} and Y{sup {minus}} (H{sub 2}O){sub n} with n {much_gt} 1. The structure of the cluster around the ion depends sensitively on the equation of state. The authors explore the consequences of possible polymorphic states of H{sub 2}O in the liquid phase at room temperature. If there are low-lying polymorphic states, the local dipole moment and the local density will change discontinuously as a function of the radial distance from the ion, and regions of different polymorphic states will be found at different separations from the ion. Fragmentation of the cluster by vigorous shaking may break up the cluster into small domains to allow subsequent coalescence of these domains or the growth of the domains as seeds to form greater domains of polymorphic states. Further experimental and theoretical analyses are needed to study these pictures.
Date: January 1, 1998
Creator: Wong, C.Y. & Lo, S.Y.
Partner: UNT Libraries Government Documents Department

Unresolved questions in J/{psi} production and propagation in nuclei

Description: In order to understand the J/{psi} suppression arising from the possible occurrence of the quark-gluon plasma in high-energy heavy-ion collisions, it is necessary to have a comprehensive picture how the J/{psi} and its precursors are produced, what their properties after production are, and how the J/{psi} and its precursors propagate inside nuclear matter. There are unresolved questions in the descriptions of J/{psi} production and propagation. The author outlines some of these questions and discusses the approaches for their resolution.
Date: November 1, 1998
Creator: Wong, C.Y.
Partner: UNT Libraries Government Documents Department

Signatures of Quark-Gluon Plasma Phase Transition in High-Energy Nuclear Collisions

Description: In high-energy nuclear collisions, the new phase of the quark-gluon plasma is indicated by an anomalous increase in pressure, an excess of direct photon production, an excess of strangeness production, and an anomalous J/{psi} suppression. We review these signatures and discuss how recent high-energy heavy-ion experiments at CERN are consistent with the production of the quark-gluon plasma in high-energy Pb+Pb collisions.
Date: May 22, 2000
Creator: Wong, C.-Y.
Partner: UNT Libraries Government Documents Department

Relativistic Generalization of the Post-Prior Equivalence for Reaction of Composite Particles

Description: In the non-relativistic description of the reaction of composite particles, the reaction matrix is independent of the choice of post or prior forms for the interaction. We generalize this post-prior equivalence to the relativistic reaction of composite particles by using Dirac's constraint dynamics to describe the bound states and the reaction process.
Date: June 4, 2001
Creator: Wong, C.Y.
Partner: UNT Libraries Government Documents Department