arXiv subjects

Wei-Ning Zhang

Publications and source records attributed to Wei-Ning Zhang.

At least 37 records · Page 2Linked to original sources

arXiv2015

Probing Shadowed Nuclear Sea with Massive Gauge Bosons in the Future Heavy-Ion Collisions

The production of the massive bosons $Z^0$ and $W^{\pm}$ could provide an excellent tool to study cold nuclear matter effects and the modifications of nuclear parton distribution functions (nPDFs) relative to parton distribution functions (PDFs) of a free proton in high energy nuclear reactions at the LHC as well as in heavy-ion collisions (HIC) with much higher center-of mass energies available in the future colliders. In this paper we calculate the rapidity and transverse momentum distributions of the vector boson and their nuclear modification factors in p+Pb collisions at $\sqrt{s_{NN}}=63$TeV and in Pb+Pb collisions at $\sqrt{s_{NN}}=39$TeV in the framework of perturbative QCD by utilizing three parametrization sets of nPDFs: EPS09, DSSZ and nCTEQ. It is found that in heavy-ion collisions at such high colliding energies, both the rapidity distribution and the transverse momentum spectrum of vector bosons are considerably suppressed in wide kinematic regions with respect to p+p reactions due to large nuclear shadowing effect. We demonstrate that in the massive vector boson productions processes with sea quarks in the initial-state may give more contributions than those with valence quarks in the initial-state, therefore in future heavy-ion collisions the isospin effect is less pronounced and the charge asymmetry of W boson will be reduced significantly as compared to that at the LHC. Large difference between results with nCTEQ and results with EPS09 and DSSZ is observed in nuclear modifications of both rapidity and $p_T$ distributions of $Z^0$ and $W$ in the future HIC.

nucl-th↗

arXiv2015

Back-to-back correlations of boson-antiboson pairs for anisotropic expanding sources

In the hot and dense hadronic sources formed in high energy heavy ion collisions, the particle interactions in medium might lead to a measurable back-to-back correlation (BBC) of boson-antiboson pairs. We calculate the BBC functions of $ϕ\,ϕ$ and $K^+K^-$ for anisotropic expanding sources. The dependences of the BBC on the particle momentum and source expanding velocity are investigated. The results indicate that the BBC functions increase with the magnitude of particle momentum and exhibit an obvious dependence on the direction of the momentum for the anisotropic sources. As the source expanding velocity decreases, the BBC function decreases when the particle momentum is approximately perpendicular to the source velocity, and the BBC function increases when the particle momentum is approximately parallel to the source velocity.

nucl-th↗

arXiv2015

Relativistic effects on the back-to-back correlation functions of boson-antiboson pairs in high energy heavy ion collisions

We calculate the back-to-back correlation (BBC) functions of relativistic boson-antiboson pairs in high energy heavy ion collisions using the Monte Carlo method. The relativistic effects on the BBC functions of $ϕ\,ϕ$ and $K^+K^-$ pairs are investigated. The investigations indicate that the relativistic effects on the BBC functions of $K^+K^-$ pairs with large momenta are significant, and the effect is sensitive to the particle freeze-out temperature.

nucl-th↗

arXiv2015

Squeezed correlations of $ϕ$ meson pairs for hydrodynamic sources in high-energy heavy-ion collisions

In the hot and dense hadronic sources formed in high-energy heavy-ion collisions, the particle interactions in medium might lead to a squeezed back-to-back correlation (BBC) of boson-antiboson pairs. We calculate the BBC functions of $ϕϕ$ for sources evolving hydrodynamically in ($2+1$) dimensions and with longitudinal boost invariance. The BBC functions for hydrodynamic sources exhibit oscillations as a function of the particle momentum because the temporal distributions of hydrodynamic sources have sharp falls to 0 at large evolving times. The dependences of the BBC functions on the directions of the particle momentum are investigated. For transverse anisotropic sources, the BBC functions are minimum when the azimuthal angles of the particles reach 0. The BBC functions increase with decreasing absolute value of the particle pseudorapidity. The oscillations and the dependences on the particle azimuthal angle and pseudorapidity are the significant signatures for detecting the BBC in high-energy heavy-ion collisions.

nucl-th↗

arXiv2015

Productions of $Z^0$ and $W^+/W^-$ in Relativistic Heavy-Ion Collisions at the LHC

The productions of massive gauge bosons, $Z^0$ and $W^+/W^-$, in heavy-ion reactions at the LHC, provide an excellent tool to study the cold nuclear matter effects in high-energy nuclear collisions. In this paper we investigate $Z^0$ and $W^+/W^-$ productions in p+Pb and Pb+Pb at the LHC, at NLO and NNLO with DYNNLO incorporating the nuclear PDFs (nPDFs) parametrization sets EPS09 and DSSZ, within the framework of perturbative QCD. The numerical simulations of the transverse momentum spectra, rapidity dependence, and related nuclear modification factors for $Z^0$ and $W$ particles, as well as the charge asymmetry for W boson, are provided and tested against the latest experimental data. It is found that the theoretical results with EPS09 and DSSZ nPDFs can give good descriptions of the recent data on $Z^0$ and $W^{\pm}$ particles in p+Pb and Pb+Pb within the experimental error bars, though some differences between results with EPS09 and DSSZ can be observed, especially in the rapidity dependence of the $Z^0$ yield. Theoretical predictions for future measurements on $Z^0$ and $W$ in p+Pb and Pb+Pb collisions at the LHC are also provided.

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arXiv2015

Fluctuations of pion flow harmonics and HBT correlation functions in ultrarelativistic heavy ion collisions

We investigate the fluctuations of pion elliptic flow, triangular flow, and Hanbury-Brown-Twiss (HBT) correlation functions for the hydrodynamic sources with fluctuating initial conditions in the heavy ion collisions of the Au-Au at $\sqrt{s_{NN}}=200$ GeV and the Pb-Pb at $\sqrt{s_{NN}} =2.76$ TeV. A method based on event-subcollection analysis is used to detect these fluctuations in ultrarelativistic heavy ion collisions. We introduce a granularity length to describe the granular inhomogeneity of the initial sources, and investigate its relationships with the fluctuations of the flow harmonics and HBT correlation functions. Our investigations indicate that the fluctuations of the triangular flow of event subcollections are sensitive to the granularity length of the initial source. This dependence may provide a way to study the granular inhomogeneity of the initial source through the analyses of the fluctuations of triangular flow in ultrarelativistic heavy ion collisions.

nucl-th↗

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.

hep-ph↗

arXiv2015

Pion Transverse Momentum Spectrum, Elliptic Flow and Interferometry in the Granular Source Model in Ultra-Relativistic Heavy Ion Collisions

We systematically investigate the pion transverse momentum spectrum, elliptic flow, and Hanbury-Brown-Twiss (HBT) interferometry in the granular source model of quark-gluon plasma droplets in ultra-relativistic heavy ion collisions. The granular source model can well reproduce the experimental results of the Au-Au collisions at $\sqrt{s_{NN}}=$ 200 GeV and the Pb-Pb collisions at $\sqrt{s_{NN}} =$ 2.76 TeV with different centralities. We examine the parameters of the granular source models with an uniform and Woods-Saxon initial energy distributions in a droplet. The parameters exhibit certain regularities for collision centrality and energy.

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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.

nucl-th↗

arXiv2014

Pion transverse momentum spectrum, elliptic flow and interferometry in the granular source model for RHIC and LHC heavy ion collisions

We systematically investigate the pion transverse momentum spectrum, elliptic flow, and Hanbury-Brown-Twiss (HBT) interferometry in the granular source model for the heavy ion collisions of Au-Au at $\sqrt{s_{NN}}=$ 200 GeV and Pb-Pb at $\sqrt{s_{NN}}=$ 2.76 TeV with different centralities. The granular source model can well reproduce the experimental results of the heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). We examine the parameters involved in the granular source model. The experimental data of the momentum spectrum, elliptic flow, and HBT radii for the two collision energies and different centralities impose very strict constraints on the model parameters. They exhibit certain regularities for collision centrality and energy. The space-time structure and expansion velocities of the granular sources for the heavy ion collisions at the RHIC and LHC energies with different centralities are investigated.

nucl-th↗

arXiv2013

Chaotic parameter $λ$ in Hanbury-Brown-Twiss interferometry in an anisotropic boson gas model

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.

nucl-th↗

arXiv2012

Two-particle interferometry for the sources undergoing first-order QCD phase transition in high energy heavy ion collisions

We investigate the two-particle interferometry for the particle-emitting sources which undergo the first-order phase transition from the quark-gluon plasma with a finite baryon chemical potential to hadron resonance gas. The effects of source expansion, lifetime, and particle absorption on the transverse interferometry radii $R_{\rm out}$ and $R_{\rm side}$ are examined. We find that the emission durations of the particles become large when the system is initially located at the boundary between the mixed phase and the quark-gluon plasma. In this case, the difference between the radii $R_{\rm out}$ and $R_{\rm side}$ increases with the transverse momentum of the particle pair significantly. The ratio of $\sqrt{R_{\rm out}^2 -R_{\rm side}^2}$ to the transverse velocity of the pair is an observable for the enhancement of the emission duration.

nucl-th↗

arXiv2012

Two-pion interferometry for the granular sources in the heavy ion collisions at RHIC and LHC energies

We investigate the two-pion interferometry in ultrarelativistic heavy ion collisions in the granular source model of quark-gluon plasma droplets. The pion transverse momentum spectra and HBT radii of the granular sources agree well with the experimental data of the most central Au-Au collisions at $\sqrt{s_{NN}}=200$ GeV at RHIC and Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV at LHC. In the granular source model the larger initial system breakup time for the LHC collisions as compared to the RHIC collisions may lead to the larger HBT radii $R_{\rm out}$, $R_{\rm side}$, and $R_{\rm long}$. However, the large droplet transverse expansion and limited average relative emitting time of particles in the granular source lead to the ratio of the transverse HBT radii $R_{\rm out}/R_{\rm side} \sim 1$.

nucl-th↗

arXiv2011

Two-pion interferometry for viscous hydrodynamic sources

The space-time evolution of the (1+1)-dimensional viscous hydrodynamics with an initial quark-gluon plasma (QGP) produced in ultrarelativistic heavy ion collisions is studied numerically. The particle-emitting sources undergo a crossover transition from the QGP to hadronic gas. We take into account a usual shear viscosity for the strongly coupled QGP as well as the bulk viscosity which increases significantly in the crossover region. The two-pion Hanbury-Brown-Twiss (HBT) interferometry for the viscous hydrodynamic sources is performed. The HBT analyses indicate that the viscosity effect on the two-pion HBT results is small if only the shear viscosity is taken into consideration in the calculations. The bulk viscosity leads to a larger transverse freeze-out configuration of the pion-emitting sources, and thus increases the transverse HBT radii. The results of the longitudinal HBT radius for the source with Bjorken longitudinal scaling are consistent with the experimental data.

nucl-th↗

arXiv2010

Two-pion interferometry for granular sources

A review on the two-pion Hanbury-Brown-Twiss (HBT) interferometry in the granular source model of quark-gluon plasma droplets is presented. The characteristic quantities of the granular source extracted by imaging analysis are presented and compared with the HBT radii obtained by the usual Gaussian formula fit. The signals of granular sources are presented.

nucl-th↗

arXiv2009

Characteristic quantities of pion-emitting sources extracted by model-independent analysis in relativistic heavy ion collisions

We examine the characteristic quantities of pion-emitting sources extracted by model-independent imaging analysis in relativistic heavy ion collisions. The moments of the spatial separation of pion pair emission can provide the characteristic information about the source geometry and coherence. They are better for describing the non-Gaussian sources with granular and core-halo structures. An improved granular source model of quark-gluon plasma droplets can reproduce the main characteristics of the two-pion correlation functions and source functions in the experiment of $\sqrt{s_{\rm NN}}=200$ GeV Au+Au collisions. The transverse-momentum dependence of the normalized first-order moments of the separation for the granular source is consistent with that of the usual interferometry results of source radii, after taking into account the Lorentz contraction in the direction of transverse momentum of pion pair.

hep-ph↗

arXiv2008

Interferometry signatures for QCD first-order phase transition in heavy ion collisions at GSI-FAIR energies

Using the technique of quantum transport of the interfering pair we examine the Hanbury-Brown-Twiss (HBT) interferometry signatures for the particle-emitting sources of pions and kaons produced in the heavy ion collisions at GSI-FAIR energies. The evolution of the sources is described by relativistic hydrodynamics with the system equation of state of the first-order phase transition from quark-gluon plasma (QGP) to hadronic matter. We use quantum probability amplitudes in a path-integral formalism to calculate the two-particle correlation functions, where the effects of particle decay and multiple scattering are taken into consideration. We find that the HBT radii of kaons are smaller than those of pions for the same initial conditions. Both the HBT radii of pions and kaons increase with the system initial energy density. The HBT lifetimes of the pion and kaon sources are sensitive to the initial energy density. They are significantly prolonged when the initial energy density is tuned to the phase boundary between the QGP and mixed phase. This prolongations of the HBT lifetimes of pions and kaons may likely be observed in the heavy ion collisions with an incident energy in the GSI-FAIR energy range.

hep-ph↗

arXiv2008

Imaging of granular sources in high energy heavy ion collisions

We investigate the source imaging for a granular pion-emitting source model in high energy heavy ion collisions. The two-pion source functions of the granular sources exhibit a two-tiered structure. Using a parametrized formula of granular two-pion source function, we examine the two-tiered structure of the source functions for the imaging data of Au+Au collisions at Alternating Gradient Synchrotron (AGS) and Relativistic Heavy Ion Collider (RHIC). We find that the imaging technique introduced by Brown and Danielewicz is suitable for probing the granular structure of the sources. Our data-fitting results indicate that there is not visible granularity for the sources at AGS energies. However, the data for the RHIC collisions with the selections of $40 < {\rm centrality} < 90%$ and $0.20<k_{\rm T}<0.36$ GeV/c are better described by the model with granular emission than that of one Gaussian. The model with granular source has more parameters than the simple Gaussian, hence can describe more complicated shapes.

hep-ph↗