Xin-Nian Wang

HIJING 1.0: A Monte Carlo program for parton and particle production in high-energy hadronic and nuclear collisions

Based on QCD-inspired models for multiple jets production, we developed a Monte Carlo program to study jet and the associated particle production in high energy pp, pA and AA collisions. The physics behind the program which includes multiple minijet production, soft excitation, nuclear shadowing of parton distribution functions and jet interaction in dense matter is briefly discussed. A detailed description of the program and instructions on how to use it are given.

Landau-Pomeranchuk-Migdal effect in QCD and radiative energy loss in a quark-gluon plasma.

The non-Abelian analogue of the Landau-Pomeranchuk-Migdal effect is investigated in perturbative QCD. Extending our previous studies, the suppression of induced soft bremsstrahlung due to multiple scatterings of quarks in the spinor representation is considered. The effective formation time of gluon radiation due to the color interference is shown to depend on the color representation of the emitting parton, and an improved formula for the radiative energy loss is derived that interpolates between the factorization and Bethe-Heitler limits.

J/psi suppression in an equilibrating parton plasma

Short-distance QCD is employed to calculate the J/ensuremath{psi} survival probability in an equilibrating parton gas whose evolution is governed by a set of master rate equations. Partons in the early stage of high-energy nuclear collisions may initially not be in equilibrium, but their average transverse momentum is sufficiently high to break up a QQifmmodebarelsetextasciimacronfi{} bound state. Such a breakup during the evolution of the parton gas is shown to cause a substantial J/ensuremath{psi} suppression at both RHIC and LHC energies, using realistic estimates of the initial parton densities. The transverse momentum dependence of the suppression is also shown to be sensitive to the initial conditions and the evolution history of the parton plasma. textcopyright{} 1996 The American Physical Society.

Energy loss effects on charm and bottom production in high-energy heavy-ion collisions

We study the effect of energy loss on charm and bottom quarks in high-energy heavy-ion collisions including longitudinal expansion and partial thermalization. We find that high-p{sub {perpendicular}} heavy quarks are greatly suppressed, and consequently, high-mass dileptons from heavy quark decays are also suppressed. We consider in detail the detector geometry and single lepton energy cuts of the PHENIX detector at the Relativistic Heavy Ion Collider. Because of the longitudinal expansion, the suppressions of ee, e{mu}, and {mu}{mu} pairs resulting from the heavy quark energy loss are very different due to the different rapidity coverages and energy cuts. The assumed energy loss rate, on the order of 1 GeV/fm, results in a large suppression on dielectrons, and dielectrons from heavy quark decays become comparable or even lower than the Drell-Yan yield. It is thus possible to probe the energy loss rate of the medium using dileptons from heavy quark decays. {copyright} {ital 1998} {ital The American Physical Society}

Screening of initial parton production in ultrarelativistic heavy-ion collisions☆

Abstract Screening of initial parton production due to the presence of on-shell partons in high-energy heavy-ion collisions is discussed. It is shown that the divergent cross sections in the calculation of parton production can be regulated self-consistently without an ad hoc cut-off, and that the resultant parton production and transverse energy production rate are finite.

Color screening in relativistic heavy ion collisions

Abstract We calculate the color screening length in a non-equilibrated gluon gas formed by interacting minijets in relativistic heavy-ion collisions. We show that the screening length is too short at CERN LHC collider energy to permit the formation of independent flux-tubes or strings. The prediction for RHIC energies is somewhat ambiguous.

Perturbative gluon shadowing in heavy nuclei

We study how much gluon shadowing can be perturbatively generated through the modified QCD evolution in heavy nuclei. We model in simultaneously fusions from independent constituents and from the same constituent, both in a proton and in a large loosely bound nucleus of [ital A][similar to]200. In addition to the actual distributions at small [ital x], we study the ratios of the distributions at an initial scale [ital Q][sub 0]=2 GeV, and show that a strong nuclear shadowing can follow from the modified QCD evolution.

Kinetic equation with exact charge conservation.

A kinetic master equation for multiplicity distributions is formulated for charged particles which are created or destroyed only in pairs due to the conservation of their Abelian charge. It allows one to study time evolution of the multiplicity distributions in a relativistic many-body system with arbitrary average particle multiplicities. It is shown to reproduce 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 grand canonical results. Implications for chemical equilibration in heavy-ion collisions are also discussed.

Expansion, thermalization and entropy production in high-energy nuclear collisions

The thermalization process is studied in an expanding parton gas using the Boltzmann equation with two types of collision terms. In the relaxation time approximation we determine the criteria under which a time-dependent relaxation time leads to thermalization of the partons. We calculate the entropy production due to collisions for the general time-dependent relaxation time. In a perturbative QCD approach on the other hand, we can estimate the parton collision time and its dependence on expansion time. The effective `out of equilibrium collision time differs from the standard transport relaxation time,

Enhancement of intermediate mass dileptons from charm decays at SPS energies

tau_{rm tr}simeq(alpha_s^2ln(1/alpha_s)T)^{-1}