Probing the final and initial state in ultrarelativistic heavy ion collisions-results from the WA98 experiment

Recent results of the WA98 experiment studying 158 A GeV /sup 208/Pb+ /sup 208/Pb collisions at the CERN SPS are presented. Transverse momentum spectra of neutral pions emitted near midrapidity are studied. They exhibit an invariance of the spectral shape and a simple scaling of the yield with the number of participating nucleons for centralities with greater than about 30 participating nucleons. It is shown that neutral pion spectra are not compatible with very low freeze-out temperatures. Directed flow of protons near target rapidity is observed in semi-central collisions, the magnitude being smaller than observed at AGS energies and than RQMD model predictions. Preliminary results on photon production indicate an excess of direct photons over the hadronic decay background. (15 refs).