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The Delta(++)-resonance production in central 158 A GeV Pb-208 + Pb-208 collisions at the CERN SPS has been studied. The Delta(++) production was estimated from the invariant mass spectrum of p pi(+)-pairs by subtracting a mixed event background. The measured Delta(++) abundance is compared with the results from other experiments at lower energies, and with a model calculation assuming thermal and chemical equilibrium. (C) 2000 Elsevier Science B.V. All rights reserved.

The A/Z dependence of projectile fragmentation at relativistic energies has been studied with the ALADIN forward spectrometer at SIS. A stable beam of 124Sn and radioactive beams of 124La and 107Sn at 600 MeV per nucleon have been used in order to explore a wide range of isotopic compositions. Chemical freeze-out temperatures are found to be nearly invariant with respect to the A/Z of the produced spectator sources, consistent with predictions for expanded systems. Small Coulomb effects (\Delta T \approx 0.6 MeV) appear for residue production near the onset of multifragmentation., Comment: 11 pages, 3 figures, accepted for publ. in Phys. Rev. Lett

Bu çalışmada, İstatistiksel Çok Katlı Parçalanma Modeli kullanılarak farklı N/Z oranlarına sahip Xe, Au ve U çekirdeklerinin, donma hacmindeki nükleer çok katlı parçalanmaları incelendi. Nükleer çok katlı parçalanma sonucunda oluşan sıcak ve soğuk parçacıkların yüzey enerjilerindeki değişim ve yüzey enerji katsayısının izospin bağımlılığı incelendi. Bunun için, hesaplamalarda kullanılan çekirdeklerde, farklı yüzey enerjilerine sahip parçacık dağılımlarına karşılık gelen Ï parametreleri, kuvvet kanunu parametrizasyonu ile hesaplandı. Böylece, yüzey enerjisindeki değişimin parçacıkların kütle ve yük dağılımlarını etkilediği görüldü. Ayrıca, sıcak ortamdaki çekirdek ile izole edilmiş çekirdek arasındaki farklılığı vurgulamak için T donma sıcaklığının yanında bir de Te etkin sıcaklığı tanımlanarak, bu sıcaklık değerlerinin nükleon başına uyarma enerjileri ile değişimlerinin sıvı-gaz faz geçişi ile ilişkisi gösterildi. Düşük uyarma enerjilerine sahip çekirdeklerin nükleer çok katlı parçalanmaları sonucunda oluşan sıcak parçacıkların yüzey enerjilerinin, izole edilmiş çekirdek için bulunan değerlere benzemediği sonucuna ulaşıldı. Parçacık çok katlılığının fazla olduğu durumda yüzey enerjisinin, parçacıkların nötron içeriğinden neredeyse bağımsız hale geldiği görüldü. Hesaplamalarda elde edilen sonuçların deneysel verilerle uyumlu olduğu görüldü., In this study, nuclear multifragmentation processes of Xe, Au and U nuclei having different N/Z ratios, at the freeze-out volume, have been investigated on the basis of Statistical Multifragmentation Model (SMM). The change of surface energy and also isospin dependency of surface energy coefficient of the hot and cold fragments produced at this nuclear multifragmentation processes have been determined. For this purpose, Ï parameters which correspond to the particle distributions having different surface energy have been calculated by means of the power-law exponents. Consequently, it is found that the change of surface energy affects the mass and charge distributions of the fragments. In addition, to emphasize the difference between the isolated nuclei and nuclei in the medium, we have introduced an effective temperature Te besides the freeze-out temperature T. The relationship between the change of this effective temperature with the excitation energy per nucleon and liquid-gas phase transition has been investigated. It has been concluded that the surface energy of hot fragments produced in multifragmentation processes have different values from those the obtained for isolated nuclei at low excitations. It is also found that the surface energy becomes nearly independent of the neutron content of fragments. The results obtained in this study are in a good agreement with the experimental data.

For single particle analysis, we have measured the transverse momentum spectra and yields for π±, K±, p and p-bar at mid-rapidity in √sNN= 200 GeV Au+Au collisions over abroad momentum range with various centrality selections. Motivated by this observation that the single particle spectra are well fitted with a hydrodynamic-inspired parameterization, termed the “blast-wave” model, to extract freeze-out temperature and radial flow velocity of the particle source. From this analysis, we have obtained freeze-out temperature Tfo=108MeV and average flow velocity〈βT〉=0.57in Au + Au central collisions at √sNN=200 GeV. We also discuss binary collision scaling of pT spectra to study hard component

The Delta(++)-resonance production in central 158 A GeV Pb-208 + Pb-208 collisions at the CERN SPS has been studied. The Delta(++) production was estimated from the invariant mass spectrum of p pi(+)-pairs by subtracting a mixed event background. The measured Delta(++) abundance is compared with the results from other experiments at lower energies, and with a model calculation assuming thermal and chemical equilibrium. (C) 2000 Elsevier Science B.V. All rights reserved.