A measurement of direct photon production in 208 Pb+ 208 Pb collisions at 158 A GeV 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. 25.75.+r,13.40.-f,24.90.+p 1

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: We present the results of a study performed on the interactions of 10.6A GeV gold nuclei in nuclear emulsions. In a minimum bias sample of 1311 interactions, 5260 helium nuclei and 2622 heavy fragments were observed as Au projectile fragments. The experimental data are analyzed with particular emphasis of target separation interactions in emulsions and study of critical exponents. Multiplicity distributions of the fast-moving projectile fragments are investigated. Charged fragment moments, conditional moments as well as two and three -body asymmetries of the fast moving projectile particles are determined in terms of the total charge remaining bound in the multiply charged projectile fragments. Some differences in the average yields of helium nuclei and heavier fragments are observed, which may be attributed to a target effect. However, two and three-body asymmetries and conditional moments indicate that the breakup mechanism of the projectile seems to be independent of target mass. We looked for evidence of critical point observable in finite nuclei by study the resulting charged fragments distributions. We have obtained the values for the critical exponents γ, β and τ and compare our results with those at lower energy experiment (1.0A GeV data). The values suggest that a phase transition like behavior, is observed .

S+Au interactions at 200,4 GeV were observed using emulsion chambers, permitting measurement of pseudorapidities in the central region with precision --0.01 unit. Scaled-factorial-moment analyses are extended to bin sizes smaller than those accessible to other fixed-target experimental techniques. For a sample of 151 central collisions, moments are calculated using both "horizontal" and "vertical" analysis techniques. While the moments are found to rise (in a log-log plot) with decreasing pseudorapidity bin size 8rf, their slopes roll off to approximately zero for 8rj < 0.1.

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