arXiv subjects

S. M. H. Wong

Publications and source records attributed to S. M. H. Wong.

42 records · Page 3Linked to original sources

arXiv1997

Equilibration in Heavy Ion Collisions at LHC and at RHIC

We consider the evolution of a parton plasma created in Au+Au collisions at LHC and at RHIC energies. Using Boltzmann equation, relaxation time approximation and perturbative QCD, we show the physics of both thermal and chemical equilibration in a transparent manner. In particular, we show inelastic processes are, contrary to common assumption, more important than elastic processes, the state of equilibration of the system can compensate for some powers of $\a_s$ for the purpose of equilibration, the two-stage equilibration scenario is, barring any unknown non-perturbative effects, inevitable and is an intrinsic feature of perturbative QCD, and gluon multiplication is the leading process for entropy generation.

nucl-th↗

arXiv1996

Thermal and Chemical Equilibration in Relativistic Heavy Ion Collisions

We investigate the thermalization and the chemical equilibration of a parton plasma created from Au+Au collision at LHC and RHIC energies starting from the early moment when the particle momentum distributions in the central region become for the first time isotropic due to longitudinal cooling. Using the relaxation time approximation for the collision terms in the Boltzmann equations for gluons and for quarks and the real collision terms constructed from the simplest QCD interactions, we show that the collision times have the right behaviour for equilibration. The magnitude of the quark (antiquark) collision time remains bigger than the gluon collision time throughout the lifetime of the plasma so that gluons are equilibrating faster than quarks both chemically and kinetically. That is we have a two-stage equilibration scenario as has been pointed out already by Shuryak sometimes ago. Full kinetic equilibration is however slow and chemical equilibration cannot be completed before the onset of the deconfinement phase transition assumed to be at $T_c=200$ MeV. By comparing the collision entropy density rates of the different processes, we show explicitly that inelastic processes, and \emph{not} elastic processes as is commonly assumed, are dominant in the equilibration of the plasma and that gluon branching leads the other processes in entropy generation. We also show that, within perturbative QCD, processes with higher power in α_s need not be less important for the purpose of equilibration than those with lower power. The state of equilibration of the system has also a role to play. We compare our results with those of the parton cascade model.

hep-ph↗

arXiv1996

Thermal and chemical equilibration in a gluon plasma

We show the evolution of a gluon plasma towards equilibrium starting at some early moment when the momentum distribution in the central region is momentaneously isotropic. Using HIJING results for Au+Au collision as initial input, we consider thermalization and chemical equilibration simultaneously at both LHC and RHIC energies. Thermalization is shown to be driven chiefly by inelastic process in our scenario contradicting common assumption that this is the role of elastic process. We argue that only the inelastic dominancy depends on the initial conditions but not the dominance itself.

hep-ph↗

arXiv1995

Debye Screening, KMS and Imaginary-Time Formalism of Temporal Axial Gauge

We argue that in QCD, the Debye mass requires not only a mathematical definition but also a physical one and temporal axial gauge could provide for a physical screening potential for this purpose. Unfortunately, this gauge is spoiled by problem of energy conservation rather than the well known divergence due to the double pole in the longitudinal propagator. We also show that KMS condition is violated in this gauge and is therefore not universally true.

hep-ph↗

arXiv1995

Difficulties in Formulating an imaginary-time formalism of temporal axial gauge at finite T

Following the successful construction of the finite T real-time formalism in temporal axial gauge, we attempt to further study the equivalent new imaginary-time formalism of James and Landshoff based on the same Hamiltonian approach in the hope that it will provide the answer to Debye screening in QCD. It turns out that, unlike in the real-time case, energy conservation does not hold because of the unusual representation of the longitudinal field forced upon by the Hamiltonian formulation.

hep-th↗

arXiv1994

Non-Debye Screening in Finite Temperature QCD

We study the non-abelian, gauge invariant, screening potential between two charges in a quark-gluon plasma. Using Braaten and Pisarski resummed perturbation theory in temporal axial gauge, we find a repulsive power screened potential which behaves as $\sim 1/r^6$ at large distance. This questions either the physical meaning of the Debye mass or the known pragmatic treatment of the temporal axial gauge propagator.

hep-ph↗