The dynamical string-parton model of relativistic heavy-ion collisions is reviewed. Features of the existing model include: 1) the strings evolve dynamically in time according to the classical Nambu-Got\=o string Lagrangian; 2) strings decay probabilistically based on the string's action integral with fragmentation parameters tuned to fit the e^+e^- data; 3) the masses of the final states are phenomenologically quantized at the physical hadronic masses; 4) initial state nucleons are composed of a distribution of string solutions determined from the measured electromagnetic structure function; 5) the interaction of strings is modeled in terms of soft quark-quark interactions and exchanges. Recent additions to the model are 1) inclusion of both soft and hard quark-quark interactions, 2) quark-quark interactions during the hadronization process, and 3) elastic hadron-hadron scattering. The role of these additional processes in p-A and A-A collisions will be elucidated.
[B17.002] Application of String-Parton Model to Proton-Nucleus and Nucleus-Nucleus Collisions
D.E. Malov, A.S. Umar, D.J. Ernst (Department of Physics and Astronomy, Vanderbilt University), D.J. Dean (Physics Division, Oak Ridge National Laboratory)
Various proton-nucleus and nucleus-nucleus collisons are considered within the dynamical string-parton model (SPM). The evolution of hadronic matter during relativistic A+A collisions is modeled in real time in terms of the dynamical degrees of freedom of the constituent quarks and gluons. Results will be presented for proton-proton collisions at ISR center-of-mass energies of 22 to 62 GeV; minimum bias p+S and p+Au collisions at 200 GeV per nucleon; central S+S, S+Au collisions at 200 GeV per nucleon; Pb+Pb collisions at 158 GeV per nucleon; and Au+Au collisions at 200 GeV per nucleon.
[B17.003] Cross sections for the dissociation of J/\psi and \psi' by \pi and \rho at low energies
C-Y. Wong (ORNL), E.S. Swanson (U. Pittsburg, JLab), T. Barnes (ORNL^*, U. Tennessee, U. Bonn, IFK Jülich)
The cross sections for the dissociation of J/\psi and \psi' by \pi and \rho at low energies are very important quantities for the interpretation of J/\psi and \psi' suppression in high-energy heavy-ion collisions. We evaluate these cross sections by using the quark-interchange model of Barnes and Swanson(T. Barnes and E. S. Swanson, Phys. Rev. D46, 131 (1992)). The dissociation cross section for J/\psi by \pi is found to be relatively small with a maximum near threshold of about 1 mb. The pion-induced \psi' dissociation cross section is found to be much larger, about 5 mb near threshold. These results appear qualitatively consistent with experimental data on J/\psi and \psi' production in heavy-ion collisions. Dissociation cross sections for J/\psi and \psi' by \rho mesons are also evaluated and are found to be large near threshold.
Managed by Lockheed Martin Energy Research Corp. for the U. S. Departmenmt of Energy Under Contract Number DE-AC05-96OR22464.
[B17.004] Signatures of the induced theta vacuum state in Heavy Ion Collisions
Ariel Zhitnitsky (University of British Columbia, Vancouver.)
We expect that, in general, an arbitrary induced theta vacuum -state would be created in the heavy ion collisions, similarly to the creation of the disoriented chiral condensate (DCC) with an arbitrary isospin direction. It should be a large domain with a wrong \theta \neq 0 orientation. If a reasonably stable induced \theta state is created, it could be observed by analyzing some unusual decays of this \theta state.
We have done some numerical simulations which support the idea that the induced \theta vacuum condensate, indeed, will be created if the cooling process is very rapid and, therefore, the system is out of equilibrium (quench approximation). Therefore, the heavy ion collisions give us a unique chance for a study an unusual matter.
I suggest few simple observables which can be (hopefully)
measured on an event by event basis at RHIC, and which
uniquely determine whether the \theta vacuum state is
created.
[B17.005] \Upsilon-Suppression and Gluon Distributions in Nuclei
Athanasios Petridis (Iowa State University)
The suppression of \Upsilon production in proton-nucleus
collisions is described in terms of modifications of parton
distributions in nuclei relative to those in free nucleons
supplemented with final state dissociation. This model which
was initially developed to describe the EMC-effect also
successfully explains J/\Psi suppression. To achieve good
agreement with the \Upsilon data the gluon distributions
must be further improved at high x. The very powerful
technique of information entropy maximization is applied to
this end. In ultrarelativistic heavy ion collisions the
\Upsilon is predicted to be more suppressed than in
proton-nucleus ones.
[B17.006] Dilepton production through a_1 resonance from hot meson gas.
Ioulia Kvasnikova, Charles Gale (Physics Department, McGill University)
In the present work the dilepton production in the reactions
involving a_1, \rho-mesons and pions is studied. A
comparison of different phenomenological Lagrangians has
been done in the case of radiative decay of a_1. We also
show results using simple approach proposed by Landsberg.
[B17.007] Quantum Field Effects in DCC Dynamics
Jorgen Randrup (NSD, LBNL, UC Berkeley, CA94720)
A mean-field treatment of the linear sigma model leads to a field description in terms of quasi-pions that are endowed with an effective mass depending on both time and space. Interesting forms of the effective mass can be obtained on the basis of self-consistent semi-classical simulations of idealized scenarios relevant to the formation of disoriented chiral condensates in high-energy nuclear collisions. Employing such specific forms in the mean-field model, the associated quantum-field description is studied both formally and numerically, yielding insight into the specific quantum effects resulting from the evolving effective mass and having a bearing on the expected DCC signals.