arXiv subjects

Cheuk-Yin Wong

Publications and source records attributed to Cheuk-Yin Wong.

At least 37 records · Page 2Linked to original sources

arXiv2018

Properties of superheavy isotopes Z=120 and isotones N=184 within the Skyrme-HFB model

We study the nuclear properties of even-even superheavy $Z$=120 isotopes and $N$=184 isotones with the Skyrme Hartree-Fock-Bogoliubov (HFB)approach. Within this model we examine the deformation energy surfaces and two paths to fission: a reflection-symmetric path with elongated fission fragments (sEF) and a reflection-asymmetric path corresponding to elongated fission fragments (aEF). Furthermore, we explore the energy surfaces in the region of very large oblate deformations with toroidal nuclear density distributions. While the energy surfaces of toroidal $Z$=120 isotopes and $N$=184 isotones do not possess energy minima without angular momenta,local energy minima (toroidal high spin isomeric states) appear for many of these superheavy nuclei with specific angular momenta about the symmetry axis. We have theoretically located the toroidal high spin isomers (THSIs) of $^{302}$Og$_{184}$,$^{302}120_{182}$, $^{306}120_{186}$, and $^{306}122_{184}$.

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arXiv2017

Event-by-Event Study of Space-Time Dynamics in Flux-Tube Fragmentation

In the semi-classical description of the flux-tube fragmentation process for hadron production and hadronization in high-energy $e^+e^-$ annihilations and $pp$ collisions, the rapidity-space-time ordering and the local conservation laws of charge, flavor, and momentum provide a set of powerful tools that may allow the reconstruction of the space-time dynamics of quarks and mesons in exclusive measurements of produced hadrons, on an event-by-event basis. We propose procedures to reconstruct the space-time dynamics from event-by-event exclusive hadron data to exhibit explicitly the ordered chain of hadrons produced in a flux tube fragmentation. As a supplementary tool, we infer the average space-time coordinates of the $q$-$\bar q$ pair production vertices from the $π^-$ rapidity distribution data obtained by the NA61/SHINE Collaboration in $pp$ collisions at $\sqrt{s}$ = 6.3 to 17.3 GeV.

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arXiv2017

Toroidal high-spin isomers in the nucleus $^{304}{120}$

Strongly deformed oblate superheavy nuclei form an intriguing region where the toroidal nuclear structures may bifurcate from the oblate spheroidal shape. The bifurcation may be facilitated when the nucleus is endowed with a large angular moment about the symmetry axis with $I=I_{z}$. The toroidal high-$K$ isomeric states at their local energy minima can be theoretically predicted using the cranked self-consistent Skyrme-Hartree-Fock method. We use the cranked Skyrme-Hartree-Fock method to predict the properties of the toroidal high-spin isomers in the superheavy nucleus $^{304}{120}_{184}$.

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arXiv2017

Superheavy toroidal nuclei in the Skyrme energy functional framework

Using the Hartree-Fock-Bogoliubov (HFB) self-consistent mean-field theory with the SkM* Skyrme energy-density functional, we study nuclear structure properties of even-even superheavy nuclei (SHN) of $Z=120$ isotopes and $N=184$ isotones. The shape of the nucleus along the lowest energy curve as a function of the quadrupole moment $Q_{20}$ makes a sudden transition from the oblate spheroids (biconcave discs) to the toroidal shapes, in the region of large oblate quadrupole moments.

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arXiv2016

Signatures of Flux Tube Fragmentation and Strangeness Correlations in pp Collisions

In the fragmentation of a color flux tube in high-energy $pp$ collisions or $e^+$-$e^-$ annihilations, the production of $q$-$\bar q$ pairs along a color flux tube precedes the fragmentation of the tube. The local conservation laws in the production of these $q$-$\bar q$ pairs will lead to the correlations of adjacently produced hadrons. As a consequence, the fragmentation of a flux tube will yield a many-hadron correlation in the form of a chain of hadrons ordered in rapidity, with adjacent hadrons correlated in charges, flavor contents, and azimuthal angles. It will also lead to a two-hadron angular correlation between two hadrons with opposite charges or strangeness that is suppressed at $Δϕ\sim 0$ but enhanced at $Δϕ\sim π$, within a rapidity window $Δy $$\sim$$1/(dN/dy)$.

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arXiv2016

Nuclear annihilation by antinucleons

We examine the momentum dependence of $\bar p$$p$ and $\bar n$$p$ annihilation cross sections by considering the transmission through a nuclear potential and the $\bar p p$ Coulomb interaction. Compared to the $\bar n p$ annihilation cross section, the $\bar p p$ annihilation cross section is significantly enhanced by the Coulomb interaction for projectile momenta below $p_{\rm lab} <$ 500 MeV/$c$, and the two annihilation cross sections approach the Pomeranchuk's equality limit [JETP Lett. {\bb 30}, 423 (1956)] at $p_{\rm lab}\sim 500$ MeV/$c$. Using these elementary cross sections as the basic input data, the extended Glauber model is employed to evaluate the annihilation cross sections for $\bar n$ and $\bar p$ interaction with nuclei and the results compare well with experimental data.

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arXiv2015

Analytical Expressions for the Hard-Scattering Production of Massive Partons

We obtain explicit expressions for the two-particle differential cross section and the two-particle angular correlation function in the hard-scattering production of massive partons in order to exhibit the ``ridge" structure on the away side in the hard-scattering process. The single-particle production cross section is also obtained and compared with the ALICE experimental data for charm production in pp collisions at 7 TeV at LHC.

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arXiv2015

Theoretical studies of possible toroidal high-spin isomers in the light-mass region

We review our theoretical knowledge of possible toroidal high-spin isomers in the light mass region in 28$\le$$A$$\le$52 obtained previously in cranked Skyrme-Hartree-Fock calculations. We report additional toroidal high-spin isomers in $^{56}$Ni with $I$=114$\hbar$ and 140$\hbar$, which follow the same (multi-particle)--(multi-hole) systematics as other toroidal high-spin isomers. We examine the production of these exotic nuclei by fusion of various projectiles on $^{20}$Ne or $^{28}$Si as an active target in time-projection-chamber (TCP) experiments.

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arXiv2015

Toroidal high-spin isomers in light nuclei with N not equal to Z

The combined considerations of both the bulk liquid-drop-type behavior and the quantized aligned rotation with cranked Skyrme-Hartree-Fock approach revealed previously [Phys. Lett. B 738 (2014) 401] that even-even, N=Z, toroidal high-spin isomeric states have general occurrences for light nuclei with A between 28 and 52. We find that in this mass region there are in addition N not equal to Z toroidal high-spin isomers when the single-particle shells for neutrons and protons occur at the same cranked frequency $\hbar ω$. Examples of N not equal to Z toroidal high-spin isomers, $^{36}_{16}$S$_{20}$($I$=74$\hbar$) and $^{40}_{18}$Ar$_{22}$($I$=80,102$\hbar$), are located and examined. The systematic properties of these N not equal to Z toroidal high-spin isomers fall into the same regular (muti-particle)-(muti-hole) patterns as other N=Z toroidal high-spin isomers.

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arXiv2015

Signature of the Fragmentation of a Color Flux Tube

The production of quark-antiquark pairs along a color flux tube precedes the fragmentation of the tube. Because of local conservation laws, the production of a $q$-$\bar q$ pair will lead to correlations of adjacently produced mesons (mostly pions). Adjacently produced mesons however can be signalled by their rapidity difference $Δy$ falling within the window of $|Δy | $$\lesssim$$ 1/(dN/dy)$, on account of the space-time-rapidity ordering of produced mesons in a flux tube fragmentation. Therefore, the local conservation laws of momentum, charge, and flavor will lead to a suppression of angular correlation function $dN/(dΔϕ\, dΔy)$ for two mesons with opposite charges or strangeness on the near side at $(Δϕ, Δy)$$ \sim$0, but an enhanced correlation on the back-to-back, away side at $Δϕ$$\sim$$ π$, within the window of $|Δy |$$\lesssim$$ 1/(dN/dy)$. These properties can be used as signatures for the fragmentation of a color flux tube. The gross features of the signature of flux tube fragmentation for two oppositely charged mesons are qualitatively consistent with the STAR and NA61/SHINE angular correlation data for two hadrons with opposite charges in the low-$p_T$ region in high-energy $pp$ collisions.

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arXiv2015

From QCD-based hard-scattering to nonextensive statistical mechanical descriptions of transverse momentum spectra in high-energy $pp$ and $p\bar p$ collisions

Transverse spectra of both jets and hadrons obtained in high-energy $pp$ and $p\bar p $ collisions at central rapidity exhibit power-law behavior of $1/p_T^n$ at high $p_T$. The power index $n$ is 4-5 for jet production and is 6-10 for hadron production. Furthermore, the hadron spectra spanning over 14 orders of magnitude down to the lowest $p_T$ region in $pp$ collisions at LHC can be adequately described by a single nonextensive statistical mechanical distribution that is widely used in other branches of science. This suggests indirectly the possible dominance of the hard-scattering process over essentially the whole $p_T$ region at central rapidity in high-energy $pp$ and $p \bar p$ collisions. We show here direct evidences of such a dominance of the hard-scattering process by investigating the power indices of UA1 and ATLAS jet spectra over an extended $p_T$ region and the two-particle correlation data of the STAR and PHENIX Collaborations in high-energy $pp$ and $p \bar p$ collisions at central rapidity. We then study how the showering of the hard-scattering product partons alters the power index of the hadron spectra and leads to a hadron distribution that may be cast into a single-particle nonextensive statistical mechanical distribution. Because of such a connection, the nonextensive statistical mechanical distribution may be considered as a lowest-order approximation of the hard-scattering of partons followed by the subsequent process of parton showering that turns the jets into hadrons, in high energy $pp$ and $p\bar p$ collisions.

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arXiv2015

Particle-hole nature of the light high-spin toroidal isomers

Nuclei under non-collective rotation with a large angular momentum above some threshold can assume a toroidal shape. In our previous work, we showed by using cranked Skyrme-Hartree-Fock approach that even-even, N=Z, high-K, toroidal isomeric states may have general occurrences for light nuclei with 28<=A<=52. We present here some additional results and systematics on the particle-hole nature of these high-spin toroidal isomers.

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arXiv2015

Chaoticity and Coherence in Bose-Einstein Condensation and Correlations

We review the properties of chaoticity and coherence in Bose-Einstein condensation and correlations, for a dense boson system in its mean-field represented approximately by a harmonic oscillator potential. The order parameter and the nature of the phase transition from the chaotic to the condensate states are studied for different fixed numbers of bosons. The two-particle correlation function in momentum space is calculated to investigate how the Bose-Einstein correlation depends on the degree of condensation and other momentum variables. We generalize the Bose-Einstein correlation analysis to three-particle correlations to show its dependence on the degree of condensation.

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arXiv2015

Longitudinal hydrodynamics from event-by-event Landau initial conditions

We investigate three-dimensional ideal hydrodynamic evolution, with Landau initial conditions, incorporating event-by-event variation with many events and transverse density inhomogeneities. We show that the transition to boost-invariant flow occurs too late for realistic setups, with corrections of $\order{20-30\%}$ expected at freezeout for most scenarios. Moreover, the deviation from boost-invariance is correlated with both transverse flow and elliptic flow, with the more highly transversely flowing regions also showing the most violation of boost invariance. Therefore, if longitudinal flow is not fully developed at the early stages of heavy ion collisions, hydrodynamics where boost-invariance holds at mid-rapidity is inadequate to extract transport coefficients of the quark-gluon plasma. We conclude by arguing that developing experimental probes of boost invariance is necessary, and suggest some promising directions in this regard.

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arXiv2014

Analytical Solutions of Landau (1+1)-Dimensional Hydrodynamics

To help guide our intuition, summarize important features, and point out essential elements, we review the analytical solutions of Landau (1+1)-dimensional hydrodynamics and exhibit the full evolution of the dynamics from the very beginning to subsequent times. Special emphasis is placed on the matching and the interplay between the Khalatnikov solution and the Riemann simple wave solution at the earliest times and in the edge regions at later times. These analytical solutions collected and developed here serve well as a useful guide and cross-check in the development of complicated numerically-intensive relativistic hydrodynamical Monte Carlo simulations.

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arXiv2014

Possible Implication of a Single Nonextensive $p_T$ Distribution for Hadron Production in High-Energy $pp$ Collisions

Multiparticle production processes in $pp$ collisions at the central rapidity region are usually considered to be divided into independent "soft" and "hard" components. The first is described by exponential (thermal-like) transverse momentum spectra in the low-$p_T$ region with a scale parameter $T$ associated with the temperature of the hadronizing system. The second is governed by a power-like distributions of transverse momenta with power index $n$ at high-$p_T$ associated with the hard scattering between partons. We show that the hard-scattering integral can be approximated as a nonextensive distribution of a quasi-power-law containing a scale parameter $T$ and a power index $n=1/(q -1)$, where $q$ is the nonextensivity parameter. We demonstrate that the whole region of transverse momenta presently measurable at LHC experiments at central rapidity (in which the observed cross sections varies by $14$ orders of magnitude down to the low $p_T$ region) can be adequately described by a single nonextensive distribution. These results suggest the dominance of the hard-scattering hadron-production process and the approximate validity of a "no-hair" statistical-mechanical description of the $p_T$ spectra for the whole $p_T$ region at central rapidity for $pp$ collisions at high-energies.

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arXiv2014

Chaoticity parameter $λ$ in two-pion interferometry in an expanding boson gas model

We investigate the chaoticity parameter $λ$ in two-pion interferometry in an expanding boson gas model. The degree of Bose-Einstein condensation of identical pions, density distributions, and Hanbury-Brown-Twiss (HBT) correlation functions are calculated for the expanding gas within the mean-field description with a harmonic oscillator potential. The results indicate that a sources with thousands of identical pions may exhibit a degree of Bose-Einstein condensation at the temperatures during the hadronic phase in relativistic heavy-ion collisions. This finite condensation may decrease the chaoticity parameter $λ$ in the two-pion interferometry measurements at low pion pair momenta, but influence only slightly the $λ$ value at high pion pair momentum.

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arXiv2014

The transverse-momenta distributions in high-energy $pp$ collisions -- A statistical-mechanical approach

We analyze LHC available data measuring the distribution probability of transverse momenta~$p_T$ in proton-proton collisions at $\sqrt{s}=0.9\,\textrm{TeV}$ (CMS, ALICE, ATLAS) and $\sqrt{s}=7\,\textrm{TeV}$ (CMS, ATLAS). A remarkably good fitting can be obtained, along fourteen decades in magnitude, by phenomenologically using $q$-statistics for a {\it single} particle of a two-dimensional relativistic ideal gas. The parameters that have been obtained by assuming $\textrm{d}N/p_T\textrm{d}p_T\textrm{d}y \propto e_q^{-E_T/T}$ at mid-rapidity are, in all cases, $q \simeq 1.1$ and $T\simeq 0.13\,\textrm{GeV}$ (which satisfactorily compares with the pion mass). This fact suggests the approximate validity of a "no-hair" statistical-mechanical description of the hard-scattering hadron-production process in which the detailed mechanisms of parton scattering, parton cascades, parton fragmentation, running coupling and other information can be subsumed under the stochastic dynamics in the lowest-order description. In addition to that basic structure, a finer analysis of the data suggests a small oscillatory structure on top of the leading $q$-exponential. The physical origin of such intriguing oscillatory behavior remains elusive, though it could be related to some sort of fractality or scale-invariance within the system.

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