235 research outputs found
Strange Particle Production from SIS to LHC
>1A review of meson emission in heavy ion collisions at incident energies
from SIS up to collider energies is presented. A statistical model assuming
chemical equilibrium and local strangeness conservation (i.e. strangeness
conservation per collision) explains most of the observed features.
Emphasis is put onto the study of and emission at low incident
energies. In the framework of this statistical model it is shown that the
experimentally observed equality of and rates at
``threshold-corrected'' energies is due to a
crossing of two excitation functions. Furthermore, the independence of the
to ratio on the number of participating nucleons observed between
SIS and RHIC is consistent with this model.
It is demonstrated that the production at SIS energies occurs
predominantly via strangeness exchange and this channel is approaching chemical
equilibrium. The observed maximum in the excitation function is
also seen in the ratio of strange to non-strange particle production. The
appearance of this maximum around 30 GeV is due to the energy
dependence of the chemical freeze-out parameters and .Comment: Presented at the International Workshop "On the Physics of the
Quark-Gluon Plasma", Palaiseau, France, September 2001. 10 pages, 8 figure
Kaon and production vs Participants in Nuclear Collisions
Data on kaon and production in nuclear collisions as a function of
centrality are analysed both at AGS and SPS energy range. We compare the
results of several experiments, looking for common trend in `participant
scaling' of production yields. We find a smooth description of scaled kaon and
yields as a function of participant density. We also show a participant
density dependence of kaons and produced in the forward hemisphere for
proton-nucleus collisions.Comment: Proceedings of the International Conference on Strangeness in Quark
Matter, 20-25 July 2000, Berkeley, CA. To appear in Journal of Physics G:
Nuclear and Particle Physic
Violation of energy-per-hadron scaling in a resonance matter
Yields of hadrons, their average masses and energies per hadron at the stage
of chemical freeze-out in (ultra)relativistic heavy-ion collisions are analyzed
within the statistical model. The violation of the scaling / = 1 GeV
observed in Au+Au collisions at = 130 AGeV is linked to the
formation of resonance-rich matter with a considerable fraction of baryons and
antibaryons. The rise of the energy-per-hadron ratio in baryon-dominated matter
is discussed. A violation of the scaling condition is predicted for a very
central zone of heavy-ion collisions at energies around 40 AGeV.Comment: 5 pages incl. 3 figures and 2 tables, to be published in Phys. Rev.
pi-/pi+ ratio in heavy ions collisions: Coulomb effect or chemical equilibration?
We calculate the pi-/pi+ ratio for Pb+Pb at CERN/SPS energies and for Au+Au
at BNL/AGS energies using a (3+1) dimensional hydrodynamical model. Without
consideration of Coulomb effect an enhancement of this ratio at low mt is found
compatible with that observed in these experiments. Our calculations are based
on previous (3+1) dimensional hydrodynamical simulations (HYLANDER), which
described many other aspects of experimental data. In this model the observed
enhancement is a consequence of baryon and strangeness conservation and of
chemical equilibration of the system and is caused by the decay of produced
hyperons, which leads to a difference in the total number of positive and
negative pions as well. Based on the same approach, we also present results for
the pi-/pi+ ratio for S+S (CERN/SPS) collisions, where we find a similar
effect. The absence of the enhancement of the pi-/pi+ ratio in the S+S data
presented by the NA44 Collaboration, if confirmed, could indicate that chemical
equilibration has not yet been estabilished in this reaction.Comment: 8 pages and 2 figures, submmited to Phys. Lett. B. This reviewed
version (Nov.29,1996) contains more details about the model simulated
efficiency considering the experimental detection conditions. Other small
modifications were mad
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Strangeness Enhancement in p-A Collisions: Consequences for the Interpretation of Strangeness Production in A-A Collisions
Published measurements of semi-inclusive Lambda production in p-Au collisions
at the AGS are used to estimate the yields of singly strange hadrons in
nucleus-nucleus A-A collisions. Results of a described extrapolation technique
are shown and compared to measurements of K+ production in Si-Al, Si-Au, and
Au-Au collisions at the AGS and net Lambda production in Su-Su, S-Ag, Pb-Pb,
and inclusive p-A collisions at the SPS. The extrapolations can account for
more than 75% of the measured strange particle yields in all of the studied
systems except for very central Au-Au collisions at the AGS where RQMD
comparisons suggest large re-scattering contributions.Comment: 9 pages, 4 figure
Strangeness dynamics in relativistic nucleus-nucleus collision
We investigate hadron production as well as transverse hadron spectra in
nucleus-nucleus collisions from 2 GeV to 21.3 TeV within two
independent transport approaches (UrQMD and HSD) that are based on quark,
diquark, string and hadronic degrees of freedom. The comparison to experimental
data demonstrates that both approaches agree quite well with each other and
with the experimental data on hadron production. The enhancement of pion
production in central Au+Au (Pb+Pb) collisions relative to scaled
collisions (the 'kink') is well described by both approaches without involving
any phase transition. However, the maximum in the ratio at 20 to 30
AGeV (the 'horn') is missed by 40%. A comparison to the
transverse mass spectra from and C+C (or Si+Si) reactions shows the
reliability of the transport models for light systems. For central Au+Au
(Pb+Pb) collisions at bombarding energies above 5 AGeV, however,
the measured -spectra have a larger inverse slope parameter
than expected from the calculations. The approximately constant slope of
spectra at SPS (the 'step') is not reproduced either. Thus the pressure
generated by hadronic interactions in the transport models above 5
AGeV is lower than observed in the experimental data. This finding
suggests that the additional pressure - as expected from lattice QCD
calculations at finite quark chemical potential and temperature - might be
generated by strong interactions in the early pre-hadronic/partonic phase of
central Au+Au (Pb+Pb) collisions.Comment: 10 pages, 5 figures, Invited talk presented by H. Stocker at
ERICE-2003 (Sep. 2003, Erice, Italy), to be published in Prog. Part. Nucl.
Phys. 52 (2004
Does HBT Measure the Freeze-out Source Distribution?
It is generally assumed that as a result of multiple scattering, the source
distribution measured in HBT interferometry corresponds to a chaotic source at
freeze-out. This assumption is subject to question as effects of multiple
scattering in HBT measurements must be investigated within a quantum-mechanical
framework. Applying the Glauber multiple scattering theory at high energies and
the optical model at lower energies, we find that multiple scattering leads to
an effective HBT density distribution that depends on the initial chaotic
source distribution with an absorption.Comment: 4 pages, talk presented at QM2004 Conference, January 11-17, 2004,
Oakland, California, USA, to be published in the Proceeding
Studies of multiplicity in relativistic heavy-ion collisions
In this talk I'll review the present status of charged particle multiplicity
measurements from heavy-ion collisions. The characteristic features of
multiplicity distributions obtained in Au+Au collisions will be discussed in
terms of collision centrality and energy and compared to those of p+p
collisions. Multiplicity measurements of d+Au collisions at 200 GeV
nucleon-nucleon center-of-mass energy will also be discussed. The results will
be compared to various theoretical models and simple scaling properties of the
data will be identified.Comment: "Focus on Multiplicity" Internationsl Workshop on Particle
Multiplicity in Relativistic Heavy Ion Collisions, Bari, Italy, June 17-19,
2003, 16 pages, 15 figure
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