72 research outputs found
Scaling of Particle and Transverse Energy Production in 208Pb+208Pb collisions at 158 A GeV
Transverse energy, charged particle pseudorapidity distributions and photon
transverse momentum spectra have been studied as a function of the number of
participants (N_{part}) and the number of binary nucleon-nucleon collisions
(N_{coll}) in 158 A GeV Pb+Pb collisions over a wide impact parameter range. A
scaling of the transverse energy pseudorapidity density at midrapidity as
N_{part}^{1.08 \pm 0.06} and N_{coll}^{0.83 \pm 0.05} is observed. For the
charged particle pseudorapidity density at midrapidity we find a scaling as
N_{part}^{1.07 \pm 0.04} and N_{coll}^{0.82 \pm 0.03}. This faster than linear
scaling with N_{part} indicates a violation of the naive Wounded Nucleon Model.Comment: 13 pages, 16 figures, submitted to European Physical Journal C
(revised results for scaling exponents
Systematics of Inclusive Photon Production in 158 AGeV Pb Induced Reactions on Ni, Nb, and Pb Targets
The multiplicity of inclusive photons has been measured on an event-by-event
basis for 158 AGeV Pb induced reactions on Ni, Nb, and Pb targets. The
systematics of the pseudorapidity densities at midrapidity (rho_max) and the
width of the pseudorapidity distributions have been studied for varying
centralities for these collisions. A power law fit to the photon yield as a
function of the number of participating nucleons gives a value of 1.13+-0.03
for the exponent. The mean transverse momentum, , of photons determined
from the ratio of the measured electromagnetic transverse energy and photon
multiplicity, remains almost constant with increasing rho_max. Results are
compared with model predictions.Comment: 16 pages including 4 figure
Direct Photon Production in 158 AGeV Pb+Pb Collisions
A measurement of direct photon production in Pb+Pb collisions at 158 AGeV has
been carried out in the CERN WA98 experiment. The invariant yield of direct
photons in central collisions is extracted as a function of transverse momentum
in the interval 0.5 < pT < 4 GeV/c. A significant direct photon signal,
compared to statistical and systematical errors, is seen at pT > 1.5 GeV/c. The
results constitute the first observation of direct photons in ultrarelativistic
heavy-ion collisions which could be significant for diagnosis of quark gluon
plasma formation.Comment: Talk presented at Nucleus-Nucleus 2000, Strasbourg, Franc
Central Collisions of Au on Au at 150, 250 and 400 A MeV
Collisions of Au on Au at incident energies of 150, 250 and 400 A MeV were
studied with the FOPI-facility at GSI Darmstadt. Nuclear charge (Z < 16) and
velocity of the products were detected with full azimuthal acceptance at
laboratory angles of 1-30 degrees. Isotope separated light charged particles
were measured with movable multiple telescopes in an angular range of 6-90
degrees. Central collisions representing about 1 % of the reaction cross
section were selected by requiring high total transverse energy, but vanishing
sideflow. The velocity space distributions and yields of the emitted fragments
are reported. The data are analysed in terms of a thermal model including
radial flow. A comparison with predictions of the Quantum Molecular Model is
presented.Comment: LateX text 62 pages, plus six Postscript files with a total of 34
figures, accepted by Nucl.Phys.
Freeze-Out Parameters in Central 158AGeV Pb+Pb Collisions
Neutral pion production in central 158AGeV Pb+Pb collisions has been studied
in the WA98 experiment at the CERN SPS. The pi0 transverse mass spectrum has
been analyzed in terms of a thermal model with hydrodynamic expansion. The high
accuracy and large kinematic coverage of the measurement allow to limit
previously noted ambiguities in the extracted freeze-out parameters. The
results are shown to be sensitive to the shape of the velocity distribution at
freeze-out.Comment: 5 pages including 3 figures, small changes due to review process,
accepted for publication in Phys.Rev.Let
Entropy production in the Au + Au reaction between 150 and 800 A MeV
The entropy per nucleon (S/A) has been extracted for the Au [(150—800)A MeV] + Au reaction by using the phase I setup of the 4 pi facility at GSI, Darmstadt. The entropy has been obtained from the comparison of various observables characterizing the dM/dZ fragment multiplicity distributions, extending up to Z~15, with those calculated with the quantum statistical model. It is the first time that S/A values are determined by considering the full ensemble of charged products detected in the reaction. Consistent values of S/A are found from different methods. These entropy values are shown to be fairly independent of the volume of the ``participant'' region considered. They are somewhat lower than those extracted in earlier works but are in good agreement with hydrodynamic calculations and suggest a low viscosity for the hot and dense nuclear matter
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