High-Multiplicity Lead-Lead Interactions at 158 GeV/c per nucleon

The Krakow-Louisiana-Minnesota-Moscow Collaboration (KLMM) has exposed a set of emulsion chambers with lead targets to a 158 GeV/{ital c} per nucleon beam of {sup 208}Pb nuclei, and we report the initial analysis of 40 high-multiplicity Pb-Pb collisions. To test the validity of the superposition model of nucleus-nucleus interactions in this new regime, we compare the shapes of the pseudorapidity distributions with FRITIOF Monte Carlo model calculations, and find close agreement for even the most central events. We characterize head-on collisions as having a mean multiplicity of 1550{plus_minus}120 and a peak pseudorapidity density of 390{plus_minus}30. These estimates are significantly lower than our FRITIOF calculations. {copyright} {ital 1996 The American Physical Society.}