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\(\cdot A\) GeV Pb+Pb collisions over a wide impact parameter range. A scaling of the transverse energy pseudorapidity density at midrapidity as \(\sim N_{part}^{1.08 \pm 0.06}\) and \(\sim N_{coll}^{0.83 \pm 0.05}\) is observed. For the charged particle pseudorapidity density at midrapidity we find a scaling as \(\sim N_{part}^{1.07 \pm 0.04}\) and \(\sim N_{coll}^{0.82 \pm 0.03}\). This faster than linear scaling with \(N_{part}\) indicates a violation of the naive Wounded Nucleon Model.
Anisotropic transverse flow has been studied with a magnetic spectrometer at midrapidity and the Plastic Ball detector at target rapidity in the WA98 experiment. Our preliminary results show the ...existence of directed and elliptic flow in semi-central Pb+Pb collisions. The magnitude of the directed flow is found to be significantly smaller than those observed at the AGS energies.
We have studied the azimuthal angle distributions of identified charged particles near mid-rapidity region in semi-central Pb+Pb collisions at SPS energies. Our preliminary results show that π
+ ...mesons and protons seem to be emitted in the reaction plane, while out-of-plane for
K
+ mesons. This phenomenon might be explained by the existence of another possible effect such as in-medium potential as well as the collective motion.
Neutral pion production in central 158A GeV sup 208Pb+ sup 208 Pb collisions has been studied in the WA98 experiment at the CERN Super Proton Synchrotron. The pisup 0 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 one 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. copyright ital 1999 ital The American Physical Society
The
Δ
++-resonance production in central 158 A GeV
208Pb+
208Pb collisions at the CERN SPS has been studied. The
Δ
++ production was estimated from the invariant mass spectrum of p
π
+-pairs by ...subtracting a mixed event background. The measured
Δ
++ abundance is compared with the results from other experiments at lower energies, and with a model calculation assuming thermal and chemical equilibrium.
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