? Production in Pb + Pb Collisions at 158 GeV/c

? Production in Pb + Pb Collisions at 158 GeV/c
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Total Pages: 15
Release: 1997
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Using the NA49 main TPC, the central production of (? + {bar?}) hyperons has been measured in CERN SPS Pb on Pb collisions at 158 GeV/c. The preliminary ({Xi} + {bar {Xi}})/ (? + {bar {Lambda}}) ratio, studied at 2.0

Neutral Pion Production in Nucleus-nucleus Collisions at 158 and 200 GeV/nucleon

Neutral Pion Production in Nucleus-nucleus Collisions at 158 and 200 GeV/nucleon
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Total Pages: 11
Release: 1998
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Two years ago, at the 12th Winter Workshop on Nuclear Dynamics held here in Snowbird, the authors presented WA80 limits on direct photon production in 200-GeV 32S + Au collisions. It was found that the results were consistent (within 1[sigma]) with the absence of an excess of photons over those that can be accounted for by the two-photon decay branches of [pi]° and [eta] mesons and by the small photon contributions from other radiative decays. They are in the process of finalizing the direct-photon production results from collisions of lead nuclei at 158 GeV/nucleon. The author briefly discusses the status of the analysis and gives some preliminary results at the end of this talk. However, most of this presentation is concerned with a very different aspect of the photon measurements: distributions of neutral pions. In contrast to direct photons which probe initial collision conditions, hadrons, such as neutral pions, interact strongly and decouple late in the reaction evolution and, thus, provide information concerning the system at freeze out. Transverse momentum spectra at low and intermediate p{sub T} relate to thermodynamic and hydrodynamic descriptions of the hot, dense systems. In addition, the high-p{sub T} region reflects the hard-scattering regime and may help one understand initial-state particle production by forming a bridge to proton-proton and proton-nucleus results. It follows that it is essential that the [pi]° measurements cover a large p{sub T} range.

Particle Production in 158.A GeV 208Pb+208Pb Collisions

Particle Production in 158.A GeV 208Pb+208Pb Collisions
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Total Pages: 13
Release: 1999
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The production of neutral pions in 158A GeV 2°8Pb+2°8Pb collisions has been studied in the WA98 experiment. The centrality dependence of the neutral pion production is investigated. An invariance of the spectral shape and a simple scaling of the yield with the number of participating nucleons is observed for centralities with more than about 50 participants. The transverse mass spectrum is analyzed in terms of a thermal model with hydrodynamic expansion. The high accuracy and large kinematic coverage of the measurement constrains the extracted freeze-out parameters, and provides information on the freeze-out velocity profile.