Quantifying Baryon Stopping in High Energy Nuclear Collisions

We propose a numerical definition for baryon stopping in relativistic heavy ion collisions that is obtainable from final hadron rapidity distributions as well as from bremsstrahlung measurements. Thus a new channel of communication is opened between the two methods.Comment: latex 9 pages, 2 embedded PS figure

Condensation of a Strongly Interacting Parton Plasma into a Hadron Gas in High Energy Nuclear Collisions

We examine the effects of color screening on the transition of a parton plasma into a hadron gas at RHIC energies. It is found that as expected, color screening posed itself as a significant barrier for hadronization. Parton-hadron conversion would therefore be delayed and prolonged when compared to that occuring in a vacuum. Due to the on-going expansion, the resulting hadron densities are lowered. Parton equilibration is also shown to be seriously disrupted in the process.Comment: 4 pages, 2 embedded EPS figures, talk presented at Quark Matter'99, Torino, Ital

Color Octet Contribution in Exclusive P-Wave Charmonium Decay

Recent advances in our understanding of the higher-wave quarkonia have generated much interests in quarkonium physics. However most are devoted to inclusive decays and productions. Experimental data of several two-body exclusive decay channels of P-wave charmonia such as \pi \pi and p \bar p are available and some have recently been re-measured by the BES collaboration. It is not clear from the outset that color octet is needed for these exclusive channels. Indeed only color singlet has been used in the past and reasonable agreement with data was found. Contrary to these old results, we provide theoretical arguments for the inclusion of color octet and perform explicit calculations to back this up.Comment: 6 pages using espcrc2.sty, contribution to the 4th Int. Conference on Hyperons, Charm and Beauty Hadrons, Valencia, June 200

Two-Loop Self-Energy and Multiple Scattering at Finite Temperature

One and two loop self-energies are worked out explicitly for a heavy scalar field interacting weakly with a light self-interacting scalar field at finite temperature. The ring/daisy diagrams and a set of necklace diagrams can be summed simultaneously. This simple model serves to illustrate the connection between multi-loop self-energy diagrams and multiple scattering in a medium.Comment: 15 pages including 7 figures; v2. with appendix added, accepted by PR

Baryonic coherent state formation from small domain disoriented chiral condensates

Rare hyperon yields such as the Omega and AntiOmega in heavy ion collision experiments are hard to be reproduced by numerical models. This, in combination with the thermal fit to SPS data, seems to call for a new production mechanism beyond the usual ones. Small domain disoriented chiral condensates (DCC) were proposed to be such a source of rare hyperons through skyrmion formation at the chiral phase transition. Here skyrmions are treated as coherent states of baryons on a compact manifold so that the distribution of baryons produced from a skyrmion can be known. From this more refined treatment, the number of topological defects produced are more than doubled to 30 or more and the domain size at the SPS is found to be even smaller than before at 1.1--1.5 fm. IT IS IMPERATIVE THEREFORE NOT TO USE ONLY PION DISTRIBUTION BUT OTHER MEANS FOR OBSERVING DCC.Comment: Talk presented at Quark Matter 2002, Nantes, France, July 2002, to appear in the proceeding

B_c Meson Production in Nuclear Collisions at RHIC

We study quantitatively the formation and evolution of B_c bound states in a space-time domain of deconfined quarks and gluons (quark-gluon plasma, QGP). At the Relativistic Heavy Ion Collider (RHIC) one expects for the first time that typical central collisions will result in multiple pairs of heavy (in this case charmed) quarks. This provides a new mechanism for the formation of heavy quarkonia which depends on the properties of the deconfined region. We find typical enhancements of about 500 fold for the B_c production yields over expectations from the elementary coherent hadronic B_c-meson production scenario. The final population of bound states may serve as a probe of the plasma phase parameters.Comment: 9 Pages, 11 Postscript Figure

Scattering amplitudes at finite temperature

We present a simple set of rules for obtaining the imaginary part of a self energy diagram at finite temperature in terms of diagrams that correspond to physical scattering amplitudes.Comment: 23 pages in Revtex, with 33 eps-figure

Soft Photon Production Rate in Resummed Perturbation Theory of High Temperature QCD

We calculate the production rate of soft real photons from a hot quark -- gluon plasma using Braaten -- Pisarski's perturbative resummation method. To leading order in the QCD coupling constant $g$ we find a logarithmically divergent result for photon energies of order $gT$, where $T$ is the plasma temperature. This divergent behaviour is due to unscreened mass singularities in the effective hard thermal loop vertices in the case of a massless external photon.Comment: 13 pages (2 figures not included), PLAINTEX, LPTHE-Orsay 93/46, BI-TP 93/5

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.Comment: 14 pages + 4 postscript figures, latex2e file, final version to appear in Nucl. Phys.

Extension of the JIMWLK Equation in the Low Gluon Density Region

It has recently been realized that the Balitsky-JIMWLK equations have serious shortcomings as equations to be used in small-x evolution near the unitarity limit. A recent generalization of the Balitsky equations has been given which corrects these shortcomings. In this paper we present an equivalent discussion, but in terms of the JIMWLK equation where we show that a new (fourth order functional derivative) term should be included. We also present a stochastic version of the new equation which, however, has some unusual mathematical aspects which are not as yet well understood.Comment: 23 pages, 1 figure, corrected typos, corrected references, published versio