FIRST RESULTS OF THE NA49 EVENT-BY-EVENT ANALYSIS OF Pb+Pb COLLISIONS AT THE SPS

We present the first results of the NA49 experiment on the eventby -event analysis of central Pb+Pb collisions at 158 GeV/N. Using the information on particle momentum and mass determined for more than 1000 charged particles in the hadronic final state of each collision, we define a set of event-by-event observables which characterize the phasespace distribution and chemical composition of the event. A statistical analysis of the resulting event spectra allows us to determine the degree of dynamical fluctuations between events evolving from similar initial conditions. This analysis reveals information on the approach to thermal and chemical equilibration in the evolution of the reaction and provides a tool to search for rare 'anomalous' events. Our present study of event-by-event fluctuations at large scales in momentum space demonstrates that correlations that are present in p+p collisions are partially dissolved in collisions of large nuclei. This gives us a quantitative measure for ..