600 research outputs found
Properties of an equilibrium hadron gas subjected to the adiabatic longitudinal expansion
We consider an ideal gas of massive hadrons in thermal and chemical
equilibrium. The gas expands longitudinally in an adiabatic way. This evolution
for a baryonless gas reduces to a hydrodynamic expansion. Cooling process is
parametrized by the sound velocity. The sound velocity is temperature dependent
and is strongly influenced by hadron mass spectrum.Comment: 7pages, 7 figures-- uucoded file of figures appended at the end,
separated from the paper by lines with many dashe
Boundary and expansion effects on two-pion correlation functions in relativistic heavy-ion collisions
We examine the effects that a confining boundary together with hydrodynamical
expansion play on two-pion distributions in relativistic heavy-ion collisions.
We show that the effects arise from the introduction of further correlations
due both to collective motion and the system's finite size. As is well known,
the former leads to a reduction in the apparent source radius with increasing
average pair momentum K. However, for small K, the presence of the boundary
leads to a decrease of the apparent source radius with decreasing K. These two
competing effects produce a maximum for the effective source radius as a
function of K.Comment: 6 pages, 5 Eps figures, uses RevTeX and epsfi
Hydrodynamical assessment of 200 AGeV collisions
We are analyzing the hydrodynamics of 200 A GeV S+S collisions using a new
approach which tries to quantify the uncertainties arising from the specific
implementation of the hydrodynamical model. Based on a previous
phenomenological analysis we use the global hydrodynamics model to show that
the amount of initial flow, or initial energy density, cannot be determined
from the hadronic momentum spectra. We additionally find that almost always a
sizeable transverse flow deve- lops, which causes the system to freeze out,
thereby limiting the flow velocity in itself. This freeze-out dominance in turn
makes a distinction between a plasma and a hadron resonance gas equation of
state very difficult, whereas a pure pion gas can easily be ruled out from
present data. To complete the picture we also analyze particle multiplicity
data, which suggest that chemical equilibrium is not reached with respect to
the strange particles. However, the over- population of pions seems to be at
most moderate, with a pion chemical potential far away from the Bose
divergence.Comment: 19 pages, 11 figs in separate uuencoded file, for LateX, epsf.tex,
dvips, TPR-94-5 and BNL-(no number yet
Kaon and Antikaon Production in Heavy Ion Collisions at 1.5 AGeV
At the Kaon Spectrometer KaoS at SIS, GSI the production of kaons and
antikaons in heavy ion reactions at a beam energy of 1.5 AGeV has been measured
for the collision systems Ni+Ni and Au+Au. The K-/K+ ratio is found to be
constant for both systems and as a function of impact parameter but the slopes
of K+ and K- spectra differ for all impact parameters. Furthermore the
respective polar angle distributions will be presented as a function of
centrality.Comment: 4 pages, 4 figures, SQM2001 in Frankfurt, Sept.2001, submitted to
Journal of Physics
K+ and K- production in heavy-ion collisions at SIS-energies
The production and the propagation of K+ and of K- mesons in heavy-ion
collisions at beam energies of 1 to 2 AGeV have systematically been
investigated with the Kaon Spectrometer KaoS at the SIS at the GSI. The ratio
of the K+ production excitation function for Au+Au and for C+C reactions
increases with decreasing beam energy, which is expected for a soft nuclear
equation-of-state. At 1.5 AGeV a comprehensive study of the K+ and of the K-
emission as a function of the size of the collision system, of the collision
centrality, of the kaon energy, and of the polar emission angle has been
performed. The K-/K+ ratio is found to be nearly constant as a function of the
collision centrality. The spectral slopes and the polar emission patterns are
different for K- and for K+. These observations indicate that K+ mesons
decouple earlier from the reaction zone than K- mesons.Comment: invited talk given at the SQM2003 conference in Atlantic Beach, USA
(March 2003), to be published in Journal of Physics G, 10pages, 7 figure
Evidence for Different Freeze-Out Radii of High- and Low-Energy Pions Emitted in Au+Au Collisions at 1 GeV/nucleon
Double differential production cross sections of negative and positive pions
and the number of participating protons have been measured in central Au+Au
collisions at 1 GeV per nucleon incident energy. At low pion energies the pi^-
yield is strongly enhanced over the pi^+ yield. The energy dependence of the
pi^-/pi^+ ratio is assigned to the Coulomb interaction of the charged pions
with the protons in the reaction zone. The deduced Coulomb potential increases
with increasing pion c.m. energy. This behavior indicates different freeze-out
radii for different pion energies in the c.m.~frame.Comment: IKDA is the Institute for Nuclear Physics in Darmstadt/German
Rapidity losses in heavy-ion collisions from AGS to RHIC energies
We study the rapidity losses in central heavy-ion collisions from AGS to RHIC
energies with the mean rapidity determined from the projectile net-baryon
distribution after collisions. The projectile net-baryon distribution in the
full rapidity range was obtained by removing the target contribution
phenomenologically at forward rapidity region from the experimental net-baryon
measurements and taking into account the projectile contribution at backward
rapidity region. Based on the full projectile net-baryon distributions,
calculation results show that the rapidity loss stops increasing from the SPS
top energy to RHIC energies, indicating that baryon transport does not depend
strongly on energy at high energies.Comment: 7 pages, 4 figure
First Measurement of Antikaon Phase-Space Distributions in Nucleus-Nucleus Collisions at Subthreshold Beam Energies
Differential production cross sections of K and K mesons have been
measured as function of the polar emission angle in Ni+Ni collisions at a beam
energy of 1.93 AGeV. In near-central collisions, the spectral shapes and the
widths of the rapidity distributions of K and K mesons are in agreement
with the assumption of isotropic emission. In non-central collisions, the K
and K rapidity distributions are broader than expected for a single thermal
source. In this case, the polar angle distributions are strongly
forward-backward peaked and the nonisotropic contribution to the total yield is
about one third both for K and K mesons. The K/K ratio is found
to be about 0.03 independent of the centrality of the reaction. This value is
significantly larger than predicted by microscopic transport calculations if
in-medium modifications of K mesons are neglected.Comment: 16 pages, 3 figures, accepted for publication in Physics Letters
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