2,610 research outputs found
Hyperon Enhancement in the Dual Parton Model
We review the two sources of hyperon enhancement in the dual parton model:
strings originating from diquark-antidiquark pairs in the nucleon sea and net
baryons containing two or three sea quarks with a yield controlled by the
observed stopping. We show that adding final state interactions (including
strangeness exchange reactions as well as the inverse reactions required by
detailed balance) with a single averaged cross-section mb, we can
explain the observed hyperon enhancement in PbPb collisions at CERN SPS.Comment: 6 pages, 2 eps-figure
Centrality Dependence of Hadron Multiplicities in Nuclear Collisions in the Dual Parton Model
We show that, even in purely soft processes, the hadronic multiplicity in
nucleus-nucleus interactions contains a term that scales with the number of
binary collisions. In the absence of shadowing corrections, this term dominates
at mid rapidities and high energies. Shadowing corrections are calculated as a
function of impact parameter and the centrality dependence of mid-rapidity
multiplicities is determined. The multiplicity per participant increases with
centrality with a rate that increases between SPS and RHIC energies, in
agreement with experiment.Comment: 15 pages, 4 postscript figure
Mechanisms of multiparticle production in heavy ion collisions at high energy
In the framework of a microscopic string model inclusive charged particle
distribution and baryon and antibaryon production are described. The emphasis
is put on high energies (RHIC) where shadowing corrections play a crucial role.
Some recent developments on suppression at CERN-SPS are also
discussed. Possible consequences for the crucial issue of thermal equilibration
of the produced system are considered.Comment: 35 pages, Latex style, 12 Figures, 2 Tables. To be published in a
special issue of ``Acta Physica Polonica'' in homage to Jan Kwiecinsk
Coherence Effects in Charmonium Production off Nuclei : Consequences for J/\psi Suppression
The probabilistic Glauber formula for nuclear absorption used in the
literature is only valid at low energies and . Due to energy
conservation, is replaced by an effective cross-section
( which
increases with and tends to the total cross-section
. Experimental data can be described with mb and mb. At high energies,
due to the increase of the coherence length, this formula changes. The main
change is the replacement of by -- for all
values of , as . Thus, if the suppression due to nuclear interaction will increase
with energy.Comment: Talk presented at the International Workshop on Charm Production,
ECT*, Trento, June 200
Nucleus-nucleus collisions: what we have learned from the heavy ion program at CERN
In the first part, I give a brief description of the quark-gluon plasma
search at CERN and of some experimental results. In the second part, I review a
dynamical model of nucleus-nucleus interactions and propose a physical
interpretation of those results.Comment: LaTeX, 11 pages, uses fleqn.sty and espcrc2.sty. Figures available
from the author. Invited talk at the XVth European Cosmic Ray Symposium,
Perpignan (France), August 1996; to appear in the proceeding
J/ suppression at 200 GeV in the comovers interaction model
The yield of per binary nucleon-nucleon collision in and
collisions at GeV is computed in the framework of the
dual parton model, supplemented with final state interaction (comovers
interaction). For the latter we use the same value of the cross-section,
mb, which describes the anomalous suppression
observed at CERN-SPS energies. Several possibilities for the value of the
absorptive cross-section are considered. Shadowing is introduced in both the
comovers and the yields. A comparison with the results at CERN-SPS,
including a prediction for collisions, is also presented.Comment: 15 pages, 3 figure
Charged Multiplicities at SPS and RHIC and consequences for suppression
Hadron multiplicities in nucleus--nucleus interactions are calculated in the
Dual Parton Model and its dependence on the number of collisions and the number
of participants is analyzed. Shadowing corrections are calculated as a function
of impact parameter and the multiplicity per participant as a funtion of
centrality is found to be in agreement with experiment at SPS and RHIC
energies. The obtained results are used to compute the suppression in
a comover approach.Comment: 4 pages, 4 postscript figures. Talk given at XXXVI Rencontres de
Moriond, Les Arcs, France, March 200
Baryon stopping and hyperon enhancement in the improved dual parton model
We present an improved version of the dual parton model which contains a new
realization of the diquark breaking mechanism of baryon stopping. We reproduce
in this way the net baryon yield in nuclear collisions. The model, which also
considers strings originating from diquark-antidiquark pairs in the nucleon
sea, reproduces the observed yields of p and Lambda and their antiparticles and
underestimates cascades by less than 50 %. However, Omega's are underestimated
by a factor five. Agreement with data is restored by final state interaction,
with an averaged cross-section as small as 0.14 mb. Hyperon yields increase
significantly faster than antihyperons, in agreement with experiment.Comment: 40 pages, 18 postscript figure
The Primakoff effect on a proton target
Primakoff effect offers us with a way to determine the radiative decay width
of pseudo-scalar mesons when they are photo-produced in the electromagnetic
field of hadronic systems. Taking advantage of recent developments in the Regge
description of the production of mesons in the strong hadronic field, this
paper evaluates the relative importance of the electromagnetic and the strong
amplitudes, and assesses the possibilities which become opened by modern
experimental facilities.Comment: 4 pages; 5 Figure
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