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Cheuk-Yin Wong

Publications and source records attributed to Cheuk-Yin Wong.

At least 109 records · Page 6Linked to original sources
arXiv2004

Signature of Granular Structures by Single-Event Intensity Interferometry

The observation of a granular structure in high-energy heavy-ion collisions can be used as a signature for the quark-gluon plasma phase transition, if the phase transition is first order in nature. We propose methods to detect a granular structure by the single-event intensity interferometry. We find that the correlation function from a chaotic source of granular droplets exhibits large fluctuations, with maxima and minima at relative momenta which depend on the relative coordinates of the droplet centers. The presence of this type of maxima and minima of a single-event correlation function at many relative momenta is a signature for a granular structure and a first-order QCD phase transition. We further observe that the Fourier transform of the correlation function of a granular structure exhibits maxima at the relative spatial coordinates of the droplet centers, which can provide another signature of the granular structure.

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arXiv2004

Pion Interferometry for Hydrodynamical Expanding Source with a Finite Baryon Density

We calculate the two-pion correlation function for an expanding hadron source with a finite baryon density. The space-time evolution of the source is described by relativistic hydrodynamics and the Hanbury-Brown-Twiss (HBT) radius is extracted after effects of collective expansion and multiple scattering on the HBT interferometry have been taken into account, using quantum probability amplitudes in a path-integral formalism. We find that this radius is substantially smaller than the HBT radius extracted from the freeze-out configuration.

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arXiv2004

Pion Interferometry for a Granular Source of Quark-Gluon Plasma Droplets

We examine the two-pion interferometry for a granular source of quark-gluon plasma droplets. The evolution of the droplets is described by relativistic hydrodynamics with an equation of state suggested by lattice gauge results. Pions are assumed to be emitted thermally from the droplets at the freeze-out configuration characterized by a freeze-out temperature $T_f$. We find that the HBT radius $R_{out}$ decreases if the initial size of the droplets decreases. On the other hand, $R_{side}$ depends on the droplet spatial distribution and is relatively independent of the droplet size. It increases with an increase in the width of the spatial distribution and the collective-expansion velocity of the droplets. As a result, the value of $R_{out}$ can lie close to $R_{side}$ for a granular quark-gluon plasma source. The granular model of the emitting source may provide an explanation to the RHIC HBT puzzle and may lead to a new insight into the dynamics of the quark-gluon plasma phase transition.

hep-ph↗
arXiv2004

Molecular States of Heavy Quark Mesons

We explore molecular states of two open heavy-quark mesons (Q qbar)-(qbar Q) in a quark-based model in terms of a four-body non-relativistic Hamiltonian with pairwise effective interactions. Molecular states are found in the combinations of {D, D*, B, B*} with {Dbar, Dbar*, Bbar, Bbar*}, including a weakly-bound D-Dbar* state near the threshold which may be qualitatively identified as the 3872 state observed recently by the Belle Collaboration.

hep-ph↗
arXiv2004

Does HBT Measure the Freeze-out Source Distribution?

It is generally assumed that as a result of multiple scattering, the source distribution measured in HBT interferometry corresponds to a chaotic source at freeze-out. This assumption is subject to question as effects of multiple scattering in HBT measurements must be investigated within a quantum-mechanical framework. Applying the Glauber multiple scattering theory at high energies and the optical model at lower energies, we find that multiple scattering leads to an effective HBT density distribution that depends on the initial chaotic source distribution with an absorption.

hep-ph↗
arXiv2003

Total Hadron-Hadron Cross Sections at High Energies

We calculate total hadron-hadron cross sections at high energies using the Low-Nussinov two-gluon model of the Pomeron. The gluon exchange is represented by a phenomenological potential including screened color-Coulomb, screened confining, and spin-spin interactions. We use bound-state wave functions obtained from a potential model for mesons, and a Gaussian wave function for a proton. We evaluate total cross sections for collisions involving pion, kaon, rho, phi, D, J/psi, psi', Upsilon, Upsilon', and the proton. We find that the total cross sections increase with the square of the sum of the root-mean square radii of the colliding hadrons, but there are variations arising from the spin-spin interaction. We also calculate the total cross sections of a mixed-color charmonium state on a pion and on a proton. The dependence of the total cross section on the size and the color state of the charmonium is investigated.

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arXiv2003

Intensity Interferometry for a Chaotic Source with a Collective Flow and Multiple Scattering

We study the effects of a collective flow and multiple scattering on two-particle correlation measurements in Hanbury-Brown-Twiss intensity interferometry. We find that under a collective flow the effective source distribution in a two-particle correlation measurement depends on the initial source distribution. In addition, it depends on a collective flow phase function which consists of terms that tend to cancel each other. As the detected particles traverse from the source point to the freeze-out point, they are subject to multiple scattering with medium particles. We examine the effects of multiple scattering on HBT correlations. By using the Glauber theory of multiple scattering at high energies and the optical model at intermediate energies, we find that multiple scattering leads to an absorption and an effective density distribution that depends on the initial source distribution.

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arXiv2003

Explicit Solution of the Time Evolution of the Wigner Function

Previously, an explicit solution for the time evolution of the Wigner function was presented in terms of auxiliary phase space coordinates which obey simple equations that are analogous with, but not identical to, the classical equations of motion. They can be solved easily and their solutions can be utilized to construct the time evolution of the Wigner function. In this paper, the usefulness of this explicit solution is demonstrated by solving a numerical example in which the Wigner function has strong spatial and temporal variations as well as regions with negative values. It is found that the explicit solution gives a correct description of the time evolution of the Wigner function. We examine next the pseudoparticle approximation which uses classical trajectories to evolve the Wigner function. We find that the pseudoparticle approximation reproduces the general features of the time evolution, but there are deviations. We show how these deviations can be systematically reduced by including higher-order correction terms in powers of $\hbar^2$.

quant-ph↗
arXiv2002

Anomalous J/psi suppression and charmonium dissociation cross sections

We study $J/ψ$ suppression in Pb+Pb collisions at CERN-SPS energies in hadronic matter with energy- and temperature-dependent charmonium dissociation cross sections calculated in the quark-interchange model of Barnes and Swanson. We find that the variation of J/$ψ$ survival probability from peripheral to central collisions can be explained as induced by hadronic matter absorption in central collisions.

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arXiv2002

The Role of Produced Hadrons in J/psi Suppression

Hadrons produced in high-energy heavy-ion collisions can suppress the production of J/psi and other charmonium states by charmonium spontaneous dissociation as the hot hadronic environment alters the interaction between the charm quark and charm antiquark. Furthermore, hadrons can thermalize a charmonium to excite it to higher charmonium states which subsequently dissociate spontaneously. They can also collide with a charmonium to lead to its prompt dissociation into an open charm pair.

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arXiv2002

Dissociation of Heavy Quarkonia in the Quark-Gluon Plasma

Using a temperature-dependent potential obtained from lattice gauge calculations, we study the stability of heavy quarkonia in the quark-gluon plasma. We find that only the Upsilon(1S) and the eta_b(1S) are bound in the quark-gluon plasma, and have a small binding energy. The quark-gluon plasma may be revealed by an Upsilon(1S) dilepton peak with an invariant mass close to twice the current b quark mass, which is lower than the Upsilon(1S) mass in free space. The quarkonia Upsilon(1S) and eta_b(1S) can dissociate by collision with quarks and gluons in the quark-gluon plasma. We evaluate the dissociation cross section of the Upsilon(1S) due to gluon absorption. The Upsilon(1S) and the eta_b(1S) can also dissociate spontaneously at temperatures above the dissociation temperature 1.11T_c, where T_c is the quark-gluon plasma phase transition temperature. At temperatures slightly above the dissociation temperature these states appear as resonances, which provides another signature for the quark-gluon plasma.

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arXiv2002

Form-factor dependence of the J/psi dissociation cross sections in meson exchange model

The $J/ψ$ dissociation by $π$ and $ρ$ mesons is examined in meson exchange model and compared to the quark interchange model. We found that the main difference between the predictions of the two models could be resolved by the form factors and the contact interactions in meson exchange model calculations. By adopting covariant form factors and adjusting the four-point couplings, we found that the meson exchange model could give similar predictions with the quark interchange models not only for the magnitudes but also for the energy dependence of the low-energy dissociation cross sections of the $J/ψ$ by $π$ and $ρ$ mesons. Our finding suggests a way to understand one of the discrepancies among the existing model predictions on the $J/ψ$ dissociation cross sections by light hadrons.

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arXiv2002

Dissociation of a Heavy Quarkonium at T<T_c

We examine three different ways a heavy quarkonium can dissociate at temperatures below the quark-gluon plasma phase transition temperature T_c: spontaneous dissociation, dissociation by thermalization, and dissociation by collision with hadrons. We evaluate the cross sections for the dissociation of J/psi and Upsilon in collision with pion as a function of temperature, using the quark-interchange model of Barnes and Swanson. We also evaluate the dissociation temperatures for various quarkonia, and the fraction of quarkonium lying above the dissociation threshold as a function of temperature, using an interquark potential inferred from lattice gauge calculations.

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arXiv2002

Dissociation of a Heavy Quarkonium at High Temperatures

We examine three different ways a heavy quarkonium can dissociate at high temperatures. The heavy quarkonium can dissociate spontaneously when it becomes unbound at a temperature above its dissociation temperature. Following the recent work of Digal, Petreczky, and Satz, we calculate the dissociation temperatures of heavy quarkonia taking into account the angular momentum selection rules and using a temperature-dependent potential inferred from lattice gauge calculations. We find that the selection rules change the dissociation temperatures substantially for charmonia but only slightly for bottomia. A quarkonium system in thermal equilibrium with the medium can dissociate by thermalization. The fraction of quarkonium lying above the dissociation threshold increases as temperature increases. A quarkonium can also dissociate by colliding with light hadrons. We evaluate the cross sections for the dissociation of $J/ψ$ and $Υ$ in collision with $π$ as a function of the temperature of the hadron medium, using the quark-interchange model of Barnes and Swanson. We find that as the temperature increases, the threshold energy decreases and the dissociation cross section increases.

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arXiv2001

Heavy Quarkonium Dissociation Cross Sections in Relativistic Heavy-Ion Collisions

Many of the hadron-hadron cross sections required for the study of the dynamics of matter produced in relativistic heavy-ion collisions can be calculated using the quark-interchange model. Here we evaluate the low-energy dissociation cross sections of $J/ψ$, $ψ'$, $χ$, $Υ$, and $Υ'$ in collision with $π$, $ρ$, and $K$, which are important for the interpretation of heavy-quarkonium suppression as a signature for the quark gluon plasma. These comover dissociation processes also contribute to heavy-quarkonium suppression, and must be understood and incorporated in simulations of heavy-ion collisions before QGP formation can be established through this signature.

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arXiv2000

The Relativistic N-body Problem in a Separable Two-Body Basis

We use Dirac's constraint dynamics to obtain a Hamiltonian formulation of the relativistic N-body problem in a separable two-body basis in which the particles interact pair-wise through scalar and vector interactions. The resultant N-body Hamiltonian is relativistically covariant. It can be easily separated in terms of the center-of-mass and the relative motion of any two-body subsystem. It can also be separated into an unperturbed Hamiltonian with a residual interaction. In a system of two-body composite particles, the solutions of the unperturbed Hamiltonian are relativistic two-body internal states, each of which can be obtained by solving a relativistic Schrödinger-like equation. The resultant two-body wave functions can be used as basis states to evaluate reaction matrix elements in the general N-body problem. We prove a relativistic version of the post-prior equivalence which guarantees a unique evaluation of the reaction matrix element, independent of the ways of separating the Hamiltonian into unperturbed and residual interactions. Since an arbitrary reaction matrix element involves composite particles in motion, we show explicitly how such matrix elements can be evaluated in terms of the wave functions of the composite particles and the relevant Lorentz transformations.

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arXiv2000

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

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.

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