35,514 research outputs found
Parton Cascade Description of Heavy-Ion Collisions at CERN ?
There seems to be a general consensus now that a first glimpse of a QGP-like
effect has become visible in the beautiful NA50 data on J/\psi production and
the `anomalous supression' phenomenon. On the other hand, it is still widely
believed that the dynamics of heavy-ion collisions at CERN SPS energy is
predominantly governed by soft, non-perturbative physics. This is ironic: after
all, it is unlikely that a QGP could be formed if the underlying dynamics were
essentyially soft, rather than that it requires intense quark-gluon production
with sufficient cascade-like reinteractions which drive the matter to large
density and equilibrium. Therefore, I advocate in this contribution that for
ultra-relativistic nucleus-nucleus collisions a description based on the pQCD
interactions and cascade evolution of involved partons can and should be used,
owing to the claim that short-range parton interactions play an important role
at sufficiently high beam energies, including CERN energy sqrt(s) = 20 A GeV.
Here mini-jet production which liberates of quarks and gluons cannot be
considered as an isolated rare phenomenon, but can occur quite copiously and
may lead to complex multiple cascade-type processes.Comment: Proceedings for Quark Matter 97; 4 pages including 6 postscript
figure
Comment on Transverse Mass Dependence of Partonic Dilepton Production in Ultra-Relativistic Heavy Ion Collisions
Comment on scale breaking effects in dilepton emission from partons during
the early stage of ultra-relativistic heavy ion collisionsComment: 6 pages, RevTe
Scaling of particle production with number of participants in high-energy A+A collisions in the parton-cascade model
In view of the recent WA98 data of pi0 spectra from central Pb+Pb collisions
at the CERN SPS, we analyze the production of neutral pions for A+ is the number of
participating nucleons, which we have approximated as 2A for central collisions
of identical nuclei. We argue that the deviation of \alpha (\simeq 1.2) from
unity may have its origin in the multiple scattering suffered by the partons.
We also find that the constant of proportionality in the above scaling relation
increases substantially in going from SPS to RHIC energies. This would imply
that the (semi)hard partonic activity becomes a much cleaner signal above the
soft particle production at the higher energy of RHIC, and thus much less
dependent on the (lack of) understanding of the underlying soft physics
background.Comment: 4 pages including 2 postscript figure
Multiple parton interactions in high-density QCD matter
Multiple interactions of quarks and gluons in high-energy heavy-ion
collisions may give rise to interesting phemomena of color charges propagating
in high-density QCD matter. We study the dynamics of multi-parton systems
produced in nucleus-nucleus collisions at energies corresponding the the CERN
SPS and the future BNL RHIC experiments. Due to the complexity of the
multi-particle dynamics we choose to employ the parton cascade model in order
to simulate the development of multiple parton scatterings and associated
stimulated emision processes. Our results indicate a non-linear increase with
nuclear mass A of, e.g., parton multiplicity, energy density, strangeness, and
contrast a linear A-scaling as in Glauber-type approaches. If multiple
interactions are suppressed and only single parton scatterings (no
re-interactions) are considered, we recover such a linear behavior. It remains
to be studied whether these results on the parton level can be experimentally
seen in final-state observables, such as the charged particle multiplicity, the
magnitude of produced transverse energy, or the number of produced strange
hadrons.Comment: 15 pages including 9 postscript 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
Dynamic Gluon Confinement in High Energy Processes within Effective QCD Field Theory
An effective Lagrangian approach to describe the dynamics of confinement and
symmetry breaking in the process of quark-gluon to hadron conversion is
proposed. The deconfined quark and gluon degrees of freedom of the perturbative
QCD vacuum are coupled to color neutral condensate fields representing the
non-perturbative vacuum with broken scale and chiral symmetry. As a first
application the evolution of gluons emitted by a fragmenting high energy pair from the perturbative to the non-perturbative regime with confinement
is studied. For reasonable parameter choice the solution of the equations of
motion leads to flux tube configurations with a string tension
GeV/fm.Comment: CERN-TH. 7409/94, 9 pages, 4 figures, postscript encoded with uufile
Comment on: "Transverse-Mass Dependence of Dilepton Emission from Preequilibrium and Quark-Gluon Plasma in High Energy Nucleus-Nucleus Collisions"
In a recent Letter, Geiger presents calculations of the dilepton emission
from the early stage of ultrarelativistic heavy ion collisions using the parton
cascade model (PCM). He shows that the scaling is not observed. In
this Comment, we point out that this is largely due to a defect in the PCM.Comment: 3 pages, LaTex, LBL-3526
Flash of photons from the early stage of heavy-ion collisions
The dynamics of partonic cascades may be an important aspect for particle
production in relativistic collisions of nuclei at CERN SPS and BNL RHIC
energies. Within the Parton-Cascade Model, we estimate the production of single
photons from such cascades due to scattering of quarks and gluons q g -> q
gamma, quark-antiquark annihilation q qbar -> g gamma, or gamma gamma, and from
electromagnetic brems-strahlung of quarks q -> q gamma. We find that the latter
QED branching process plays the dominant role for photon production, similarly
as the QCD branchings q -> q g and g -> g g play a crucial role for parton
multiplication. We conclude therefore that photons accompanying the parton
cascade evolution during the early stage of heavy-ion collisions shed light on
the formation of a partonic plasma.Comment: 4 pages including 3 postscript figure
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