arXiv subjects

Zi-wei Lin

Publications and source records attributed to Zi-wei Lin.

14 recordsLinked to original sources

arXiv2003

Quark Coalescence and Elliptic Flow of Charm Hadrons

Elliptic flow of charm hadrons is investigated based on the quark coalescence model. Due to the large difference between the charm quark and light quark masses, hadrons containing both light and charm quarks show a qualitatively different $v_2(p_\perp)$ from hadrons containing only light quarks. Simple relations are proposed to infer quark elliptic flow from those of hadrons. The effects of the finite momentum spread of hadron wavefunctions are also studied, and are found to be small for charm hadrons.

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arXiv2003

Deuteron-Nucleus Collisions in a Multi-Phase Transport Model

Using a multi-phase transport (AMPT) model, we study pseudo-rapidity distributions and transverse momentum spectra in deuteron-gold collisions at RHIC. We find that final-state partonic and hadronic interactions affect the transverse momentum spectrum of protons more than those of kaons or pions. Relative to p+p collisions at same center-of-mass energy per nucleon pair, the effect of final-state interactions on the charged particle transverse momentum spectra in d+Au collisions is much smaller than observed in experimental data, indicating that initial-state effects such as the Cronin effect are important.

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arXiv2003

Kaon Interferometry at RHIC from AMPT Model

The two-kaon interferometry at RHIC is studied in a multi-phase transport model. Similar to the pion case, we find strong space-time correlation at freeze-out for the kaon emission source, which results in a large positive $R_{\rm out}-t$ term and tends to reduce the $R_{\rm out}/R_{\rm side}$ ratio. Unlike the pion case, the source radii for kaons determined from the emission function are close to the radius parameters extracted from a Gaussian fit to the correlation function.

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arXiv2002

Partonic Effects on Pion Interferometry at the Relativistic Heavy Ion Collider

Using a multiphase transport (AMPT) model that includes both initial partonic and final hadronic interactions, we study the pion interferometry at the Relativistic Heavy Ion Collider. We find that the two-pion correlation function is sensitive to the magnitude of the parton scattering cross section, which controls the parton density at which the transition from the partonic to hadronic matter occurs. Also, the emission source of pions is non-Gaussian, leading to source radii that can be more than twice larger than the radius parameters extracted from a Gaussian fit to the correlation function.

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arXiv2002

Charmonium Absorption in the Meson-exchange Model

We review the meson-exchange model for charmonium absorption by hadrons. This includes the construction of the interaction Lagrangians, the determination of the coupling constants, the introduction of form factors, and the predicted cross sections for $J/ψ$ absorption by both mesons and nucleons. We further discuss the effects due to anomalous parity interactions, uncertainties in form factors, constraints from chiral symmetry, and the change of charmed meson mass in medium on the cross sections for charmonium absorption in hadronic matter.

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arXiv2002

Flavor ordering of elliptic flows at high transverse momentum

Based on the quark coalescence model for the parton-to-hadron phase transition in ultra-relativistic heavy ion collisions, we relate the elliptic flow ($v_2$) of high $\pt$ hadrons to that of high $\pt$ quarks. For high $\pt$ hadrons produced from an isospin symmetric and quark-antiquark symmetric partonic matter, magnitudes of their elliptic flows follow a flavor ordering as $(v_{2,π}=v_{2,N}) > (v_{2,Λ}=v_{2,Σ}) > v_{2,K} > v_{2,Ξ} > (v_{2,ϕ}=v_{2,Ω})$ if strange quarks have a smaller elliptic flow than light quarks. The elliptic flows of high $\pt$ hadrons further follow a simple quark counting rule if strange quarks and light quarks have same high $\pt$ spectrum and coalescence probability.

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arXiv2002

Phi meson production in relativistic heavy ion collisions

Within a multiphase transport model we study phi meson production in relativistic heavy ion collisions from both superposition of initial multiple proton-proton interactions and the secondary collisions in the produced hadronic matter. The yield of phi mesons is then reconstructed from their decaying product of either the kaon-antikaon pairs or the dimuon pairs. Since the kaon-antikaon pairs at midrapidity with low transverse momenta are predominantly rescattered or absorbed in the hadronic medium, they can not be used to reconstruct the phi meson and lead thus to a smaller reconstructed phi meson yield than that reconstructed from the dimuon channel. With in-medium mass modifications of kaons and phi mesons, the phi yield from dimuons is further enhanced compared to that from the kaon-antikaon pairs. The model result is compared with the experimental data at the CERN/SPS and RHIC energies and its implications to quark-gluon plasma formation are discussed.

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arXiv2001

Partonic effects on the elliptic flow at relativistic heavy ion collisions

The elliptic flow in heavy ion collisions at RHIC is studied in a multiphase transport model. By converting the strings in the high energy density regions into partons, we find that the final elliptic flow is sensitive to the parton scattering cross section. To reproduce the large elliptic flow observed in Au+Au collisions at $\sqrt s=130A$ GeV requires a parton scattering cross section of about 6 mb. We also study the dependence of the elliptic flow on the particle multiplicity, transverse momentum, and particle mass.

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arXiv2001

Baryon Number Fluctuation and the Quark-Gluon Plasma

We show that $ω_B$ or $ω_{\bar B}$, the squared baryon or antibaryon number fluctuation per baryon or antibaryon, is a possible signature for the quark-gluon plasma that is expected to be created in relativistic heavy ion collisions, as it is a factor of three smaller than in an equilibrated hadronic matter due to the fractional baryon number of quarks. Using kinetic equations with exact baryon number conservation, we find that their values in an equilibrated matter are half of those expected from a Poisson distribution. Effects due to finite acceptance and non-zero net baryon number are also studied.

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arXiv2001

Multistrange baryon production in relativistic heavy ion collisions

Using a multiphase transport model, we study the production of multistrange baryons from the hadronic matter formed in relativistic heavy ion collisions. The mechanism we introduce is the strangeness-exchange reactions between antikaons and hyperons. We find that these reactions contribute significantly to the production of multistrange baryons in heavy ion collisions at SPS energies, which has been found to be appreciably enhanced. We have also made predictions for multistrange baryon production in heavy ion collisions at RHIC and found a similar enhancement.

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arXiv2001

Multiphase transport model for heavy ion collisions at RHIC

Using a multiphase transport model (AMPT) with both partonic and hadronic interactions, we study the multiplicity and transverse momentum distributions of charged particles such as pions, kaons and protons in central Au+Au collisions at RHIC energies. Effects due to nuclear shadowing and jet quenching on these observables are also studied. We further show preliminary results on the production of multistrange baryons from the strangeness-exchange reactions during the hadronic stage of heavy ion collisions.

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arXiv2001

Strangeness equilibration in heavy ion collisions

Using a relativistic transport model for heavy ion collisions at energies that are below the threshold for kaon and antikaon production in nucleon-nucleon collisions, we study how their abundances approach the canonical equilibrium during the collisions. We find that kaons are far from chemical equilibrium at the initial and high density stage, and they approach equilibrium only during the expansion stage of the collisions when their production rate is small and becomes comparable to their annihilation rate. In contrast, antikaons approach chemical equilibrium much earlier but eventually fall out of equilibrium again as a result of their large annihilation cross sections in nuclear matter.

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arXiv2001

Charged particle rapidity distributions at RHIC

Using a multiphase transport model (AMPT), which includes both initial partonic and final hadronic interactions, we study the rapidity distributions of charged particles such as protons, antiprotons, pions, and kaons in heavy ion collisions at RHIC. The theoretical results for the total charged particle multiplicity at midrapidity are consistent with those measured by the PHOBOS collaboration in central Au+Au collisions at $\sqrt s$ = 56 and 130 AGeV. We find that these hadronic observables are much more sensitive to the hadronic interactions than the partonic interactions.

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arXiv2000

Kinetic equation with exact charge conservation

We formulate the kinetic master equation describing the production of charged particles which are created or destroyed only in pairs due to the conservation of their Abelian charge.Our equation applies to arbitrary particle multiplicities and reproduces the equilibrium results for both canonical (rare particles) and grand canonical (abundant particles) systems. For canonical systems, the equilibrium multiplicity is much lower and the relaxation time is much shorter than the naive extrapolation from the grand canonical ensemble results. Implications for particle chemical equilibration in heavy-ion collisions are discussed.

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